WASHINGTON -- The White House pushed forward aggressively on Monday for Congressional approval of an attack on Syria as President Obama got tentative support from one of his most hawkish Republican critics, Senator John McCain of Arizona, for a "limited" strike -- as long, Mr. McCain said, as the president did more to arm the Syrian opposition.
After an hourlong meeting with Mr. Obama at the White House, Mr. McCain emerged with Senator Lindsey Graham, Republican of South Carolina, to say that the two senators' discussions with Mr. Obama in the Oval Office had been "encouraging." He also urged Congress to support Mr. Obama in his plan for military action in Syria, saying that a no vote would be "catastrophic" for the United States and its credibility in the world.
The words from Mr. McCain were a positive development for the White House and a critical part of the Obama administration's lobbying blitz on Syria on Monday. The day got off to a start with a 70-minute telephone briefing to the House Democratic Caucus by Secretary of State John Kerry; Defense Secretary Chuck Hagel; Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff; Susan E. Rice, the national security adviser; and James R. Clapper Jr., the director of national intelligence.
There were 127 House Democrats on the call, nearly two-thirds of their total number. Democrats on the call said the debate was shifting away from whether the Assad government had used chemical weapons in a massacre last week -- several Democrats said the material cited as evidence by the administration was persuasive -- and more toward how should the administration should respond.
"The debate is shifting away from, did he use chemical weapons, to what should be done about it?" Representative Adam B. Schiff, a California Democrat on the House Intelligence Committee, said in a telephone interview.
There was also a strong sense on the call, Democrats said, that Mr. Obama needs to appeal directly to American public, most likely in a prime-time address.
On the call, Mr. Kerry took the lead, portraying the horrors of chemical weapons and underscoring the consequences of inaction. General Dempsey reviewed possible targeting, and how the military is planning strikes that minimize threat to civilians. He also reprised the argument that delay does not help President Bashar al-Assad despite his dispersal of troops and equipment. Mr. Clapper reviewed unclassified intelligence, particularly his view of why rebels could not have launched poison gas attack. Ms. Rice played maestro and traffic cop and assigned questions from lawmakers to the briefers.
Although Mr. McCain and Mr. Graham have been sharply critical of Mr. Obama that a strike he is planning on Syria would not be extensive enough, many more lawmakers in both parties have taken the opposite approach of Mr. McCain and Mr. Graham, saying they were wary of a strike on Syria, no matter how limited.
On Tuesday, Mr. Obama is to meet with the leadership of the Senate Armed Services Committee, the Senate Foreign Relations Committee, the Senate Select Committee on Intelligence, and their counterparts in the House.
Administration officials said the influential pro-Israel lobby group Aipac was already at work pressing for military action against the government of Mr. Assad, fearing that if Syria escapes American retribution for its use of chemical weapons, Iran might be emboldened in the future to attack Israel. In the House, the majority leader, Eric Cantor of Virginia, the only Jewish Republican in Congress, has long worked to challenge Democrats' traditional base among Jews.
One administration official, who, like others, declined to be identified discussing White House strategy, called Aipac "the 800-pound gorilla in the room," and said its allies in Congress had to be saying, "If the White House is not capable of enforcing this red line" against the catastrophic use of chemical weapons, "we're in trouble."
Another official, who acknowledged having deep doubts when the president disclosed on Friday night his desire for a Congressional vote -- he said he first thought, "Whoa, why are we doing this?" -- by Sunday had joined some other doubters in deciding the gambit was a good one, and would succeed.
"At the end of the day, we're not going to lose the vote," a third official said.
Given the risks, however, Mr. Obama's White House team is wasting no time seeking lawmakers' support. Although Congress is still in its summer recess, some administration officials traveled to Capitol Hill to meet with House members who might be available and wanted a briefing on Syria.
Briefers included Antony J. Blinken, the deputy national security adviser, who is a longtime aide to Vice President Joseph R. Biden Jr.; the deputy director of national intelligence, Robert Cardillo; the under secretary of defense for policy, Jim Miller; Wendy R. Sherman, the under secretary of state for policy, and Vice Adm. Kurt W. Tidd of the Joint Chiefs of Staff.
Mr. Obama and Mr. Biden, a senator for nearly four decades, will also be personally lobbying lawmakers. The White House plans to rely on supportive Republicans with intelligence backgrounds, like Representative Mike Rogers of Michigan and Senator Saxby Chambliss of Georgia, for an assist.
Although such tactics reflect an inside lobbying game, the White House will also pursue an outside game of trying to sway a skeptical American public -- as appearances by Mr. Kerry on five morning talk shows reflected. In addition, Mr. Obama will use his trip this week to St. Petersburg, Russia, for the G-20 summit meeting of major industrialized and developing countries, to publicly and privately press the case.
Despite likely opposition from senators like Rand Paul of Kentucky, the White House is somewhat sanguine about winning the vote in the Democratic-controlled Senate, with support from a majority of Democrats and enough Republicans. The House is the greater worry, in part because even its Republican leaders -- Mr. Cantor and Speaker John A. Boehner -- have had trouble in the past passing their own priority legislation in the face of independent-minded conservatives.
The rush of activity continues two days after Mr. Obama's surprise decision to announce that he would seek the authorization of Congress for a strike on the Syrian government.
Ahead of an Arab League meeting in Cairo, Mr. Kerry sought to mobilize backing for American-led military action at a meeting the group held on Sunday night.
A statement that was issued by the league asserted that the Syrian government was "fully responsible" for the chemical weapons attack and asked the United Nations and the international community "to take the necessary measures against those who committed this crime."
To the satisfaction of American officials, the statement did not explicitly mention the United Nations Security Council or assert that military action could be taken only with its approval. But it stopped short of a direct call for Western military action against Syria.
Before the meeting got under way, the Saudi foreign minister, Prince Saud al-Faisal, urged the international community to stop the Syrian government's "aggression" against its people.
Saudi Arabia has been one of the principal supporters of the Syrian opposition, and Mr. Kerry consulted by phone on Sunday with Prince Bandar bin Sultan, Saudi Arabia's intelligence chief and secretary general of its national security council.
The Obama administration's calculation has been that a call for tough action by the Arab diplomats would enable the White House to argue to members of Congress that it had regional backing for military action and would make up, at least politically, for the British decision on Thursday not to join the American-led attack.
But Syria's government on Sunday defiantly mocked Mr. Obama's decision to turn to Congress, saying it was a sign of weakness. A state-run newspaper, Al Thawra, called the action "the start of the historic American retreat" and said Mr. Obama had put off an attack because of a "sense of implicit defeat and the disappearance of his allies."
Syria's deputy foreign minister, Faisal Mekdad, told reporters in Damascus, "It is clear there was a sense of hesitation and disappointment in what was said by President Barack Obama yesterday. And it is also clear there was a sense of confusion, as well."
In some measure, part of the challenge that the Obama administration faces in trying to rally support at home for a punitive strike in Syria is the result of the deep ambivalence it has expressed about becoming involved in the conflict.
Part of the White House strategy for securing Congressional support now is to emphasize not only what Syria did, but also how a failure to act against Syria might embolden enemies of Israel like Iran and Hezbollah.
Mr. Kerry, in his television appearances, said that if Congress passed a measure authorizing the use of force, it would send a firm message to Iran that the United States would not tolerate the fielding of a nuclear device, and thus safeguard Israel's security.
"I do not believe the Congress of the United States will turn its back on this moment," Mr. Kerry said on the NBC News program "Meet The Press." "The challenge of Iran, the challenges of the region, the challenge of standing up for and standing beside our ally, Israel, helping to shore up Jordan -- all of these things are very, very powerful interests and I believe Congress will pass it."
Israeli officials have been concerned by Mr. Obama's decision, but have been mostly restrained in their public comments. Mr. Kerry talked on Sunday with Benjamin Netanyahu, the Israeli prime minister.
Both the House and Senate are expected to have votes sometime after they return from recess on Sept. 9, although Senator Harry Reid, the Democratic leader, said the Senate Foreign Relations Committee would convene hearings on the Syrian issue Tuesday afternoon.
While Mr. Kerry said he was confident Congress would vote to approve the use of force, Representative Peter T. King, the New York Republican and a former chairman of the House Homeland Security Committee, said that if a vote in the House were held today, Mr. Obama would likely lose as a result of the "isolationist wing."
Much of the debate in Washington concerned the terms of the resolution the White House has proposed for authorizing the use of force.
Representative Chris Van Hollen, a senior Democrat from Maryland, said that while the administration's resolution limited the purpose of an attack to stopping the use of weapons of mass destruction, the measure left the military too much "running room" and did not set limits on the duration of the military operation.
Congressional advocates of strong action to help the Syrian opposition, in contrast, have complained that the attack that President Obama appears to be planning seemed to be too limited to have enough of an impact.
As the White House consults with Congress, Mr. Kerry is planning a new round of diplomacy. He is planning to meet next weekend with European Union diplomats in Vilnius, Lithuania, and with Arab League diplomats in Rome.
After Mr. Obama's change in direction, the reaction in Britain and France has largely been one of surprise and confusion. The French government, which had said on Friday that it would support a military strike, said it would wait for the American Congress to vote before taking any military action.
President François Hollande still intends to proceed with a military intervention of some kind in Syria, French officials said Sunday, but France will await the decision of Congress before taking action.
"We cannot leave this crime against humanity unpunished," said Interior Minister Manuel Valls, speaking on French radio. But given logistical questions of "intervention capacity," Mr. Valls said, France must "await the decision of the United States."
"France cannot go forward alone," he said. "There must be a coalition."
A major question for military experts is what effect the delay in acting might have if force was eventually used by the United States.
Jack Keane, a former vice chief of staff of the Army and a retired four-star general, said in an interview that time would work to the advantage of President Bashar al-Assad as the Syrian forces would have more opportunities to move artillery, missiles and other equipment into civilian areas that they knew would not be struck.
Even Syrian command centers that could not be moved, he said, would be emptied of sensitive equipment and personnel.
But Mr. Obama said that he had been assured by General Dempsey that a delay would not affect the United States military's ability to carry out a strike.
Jonathan Weisman contributed reporting from Washington, David D. Kirkpatrick from Cairo, and Steven Erlanger from London.
This article originally appeared in The New York Times.