DOHA, Qatar -- Secretary of State John Kerry flew to Moscow early last month, determined to involve Russia in a new push to try to end the carnage in Syria. After a two-and-a-half-hour meeting with the Russian president, Vladimir V. Putin, and a private stroll with Sergey V. Lavrov, the Russian foreign minister, the two sides announced they would convene a conference in Geneva to bring representatives of the Syrian government together with the opposition, possibly by the end of May.
The idea of a conference was a bold move -- and so far, at least, an unsuccessful one. More than six weeks later, the Syrian opposition has suffered a stinging setback in Qusayr, the Obama administration has decided for the first time to arm the rebels, relations between the United States and Russia have taken a turn for the worse, and it is possible the Geneva meeting may never take place.
Undaunted, Mr. Kerry arrived here on Saturday to meet with his European and Middle Eastern counterparts and try again to cobble together an effective strategy to bolster the opposition, prod President Bashar al-Assad of Syria to yield power and end the fighting that has already killed more than 90,000 people. The whirlwind trip, Mr. Kerry's ninth as secretary of state, will also include stops in Jordan, Israel, Saudi Arabia, Kuwait and India and a meeting in Brunei.
While his predecessor, Hillary Rodham Clinton, was a global celebrity and possibly a future president, Mr. Kerry is striving to carve out a legacy as one of the most influential secretaries of state in recent years by taking on some of the world's most intractable problems.
Unlike Mrs. Clinton, a defeated rival who was persuaded to take the job by President Obama and for all her star power was often frustrated that policy was made in the White House, Mr. Kerry came into his administration with strong ties to Mr. Obama, whose presidential campaign he helped begin at the 2004 Democratic convention. Mr. Kerry, 69, a former chairman of the Senate Foreign Relations Committee and the son of a Foreign Service officer, has long aspired to be secretary of state. He arrived at a time when Mr. Obama has said the nation is at a "crossroads" in its relations with the world, with the Pentagon focused on ending the war in Afghanistan, the C.I.A. charged with refocusing its efforts against terrorism and the president calling for a new focus on diplomacy.
But there are also some potential obstacles for Mr. Kerry. One is the centralization of foreign policy decision-making in a White House that has famously maintained a tight grip on foreign policy -- so much so that before taking the job, Mr. Kerry received an assurance that he would be consulted before major foreign policy decisions were made. And a major one is the priorities he has set for himself, particularly Syria.
"I believe that the Syria issue will be the test of John Kerry," said Senator John McCain, Republican of Arizona, Mr. Kerry's friend and former colleague.
His other priority, reviving the Mideast talks, has proved intractable for far longer. With the Palestinians warning that they may underscore their claim to statehood by seeking membership in the International Criminal Court and other international agencies and the possibility that the Israelis' informal settlement freeze may lapse, Mr. Kerry is in a race to begin negotiations over a two-state solution before the window he is struggling to crack open is slammed shut.
Critics of the Obama administration see Mr. Kerry's focus on the Middle East as an implicit acknowledgment that the White House's widely advertised "rebalancing" to Asia is premature, and perhaps even a wishful evasion of unwelcome foreign policy realities. Supporters, though, insist there is not a contradiction.
"If you are really going to pivot to Asia, you cannot leave the Middle East in flames," said Strobe Talbott, the head of the State Department's Foreign Affairs Policy Board and president of the Brookings Institution. "With regard to Egypt, the Arab-Israel peace process, Syria, Iraq, Iran -- all of that has to be manageable."
Mr. Kerry has been tight-lipped about his strategy to jump-start direct talks between the Israelis and the Palestinians, but the main elements appear to include a way to address Israel's security concerns if new borders are agreed on, the lure of millions of dollars in investment if a Palestinian state is established and securing support from Arab nations for an eventual accord.
One precept that he has carried over from his years as a senator is that the best and perhaps only way to achieve a breakthrough is to tackle core issues as quickly as possible while avoiding getting bogged down in tangential debates over preconditions for talks. But the dominant view among Middle East experts is that the negotiations would be an uphill struggle at best, because of divisions among the Palestinians, the hard-line cast of the Israeli government and the deep skepticism each side harbors about the other's intentions.
Robert M. Danin, a senior fellow at the Council on Foreign Relations, said Mr. Kerry's diplomacy was based on the belief that "the price of inaction is too high, but the parties don't seem to share that sense of urgency."
To the issues he faces, Mr. Kerry brings a worldwide list of contacts, a dogged belief in personal diplomacy and no small measure of self-confidence.
"Kerry believes that the time for Middle East envoys is over, that by using his personal relationship with the key principals he can move the negotiating process out of the rut it has been in for four years," said Martin S. Indyk, who served as ambassador to Israel during the Clinton administration.
Mr. Kerry's hands-on approach was evident during a March visit to Turkey. After Prime Minister Recep Tayyip Erdogan appeared to undermine the prospects for an Israeli-Turkish entente by casting Zionism as a "crime against humanity" at a United Nations meeting, Mr. Kerry sought to defuse the controversy.
To make the point that Zionism was a valid nationalist movement and avoid turning the dispute into a test of wills, Mr. Kerry, who has known Mr. Erdogan since he was the mayor of Istanbul in the 1990s, took out an iPad and ran a Web search on the term.
For several minutes the two sides pored over the definition in Turkish and English, and the minicrisis was smoothed over.
But it is Syria that may prove his most difficult test. With Mr. Kerry emphasizing the importance of changing Mr. Assad's "calculation" that he can keep power, the possibility of negotiating a transitional government has been critically dependent on the military pressure Syria's opposition can put on the government. That has been a vexing issue for a White House that has proclaimed that Mr. Assad's days are numbered even as it remains anxious to turn the page on military conflicts in the Middle East.
In his meeting with Mr. Putin last month, Mr. Kerry argued that if Russia and the United States joined forces, there was no need for Syria to become another Iraq, invoking an analogy that seemed intended to appeal to Russians who have complained that the American intervention there led to a failed country.
But Mr. Kerry's push in Moscow for an international peace conference was quickly overtaken by events on the battlefield as the Assad government gained ground with the help of Hezbollah, the militant Lebanese group, and arms the Iranians have flown to Damascus through the skies of an Iraq now devoid of American forces. Suddenly, a weakened Syrian opposition faced the prospect of attending a conference to negotiate with representatives of an emboldened Assad government, and Gen. Salim Idris, the senior rebel commander, balked.
With the Syrian opposition in disarray, the Russians suggested at a recent planning meeting in Geneva that multiple opposition delegations might attend, prompting concerns that it would enable Mr. Assad's team to pursue a divide-and-conquer strategy. The United States and Lakhdar Brahimi, the United Nations special envoy, pushed back, insisting that a unified opposition team attend, participants said.
Some senior State Department officials were so concerned about the rebels' deteriorating position on the battlefield that they urged the United States to consider airstrikes against Syrian airfields to curtail the flow of arms from Iran and blunt the Assad government's air attacks. At a meeting at the White House on June 12, Mr. Kerry discussed military options with Pentagon and other administration officials.
The Pentagon and the president, however, remain deeply wary of military intervention and, for now, such options have remained on the shelf. But Mr. Obama did decide to supply ammunition, small arms and potentially antitank weapons to the rebels -- a move championed unsuccessfully by Mrs. Clinton last year and one that one Arab official said finally made the United States "a full partner" in shaping the strategy for the coalition of nations trying to oust Mr. Assad.
Obama administration officials denied that the exchanges at the meeting were confrontational. But the question remains whether the arms shipments approved by Mr. Obama and provided by partners will put sufficient pressure on the Assad government to bring a political transition or merely encourage a bloody stalemate, which could raise again the issue of whether military intervention should be considered.
As for Mr. Kerry, he has made clear from the time he joined the administration that he is not one to air his advice to the White House in public.
At his first meeting with his staff on the seventh floor of the State Department, officials say, Mr. Kerry used a Boston sports analogy to explain his role in the administration. The secretary of state would be like Bill Walton, the basketball star who helped the Celtics win a championship, and would help the Obama team by creating shots and passing the ball at the right moment.
"There's no more 'me,' only 'we,' " he told his aides.
This article originally appeared in The New York Times.