WASHINGTON -- Sen. Rick Santorum and his challenger, state Treasurer Bob Casey, clashed on the war in Iraq, terrorism and Social Security yesterday in the first televised debate of their closely watched campaign.

Their encounter on the NBC television news show "Meet the Press" produced several heated exchanges but broke little new ground on the familiar issues in the race. Mr. Santorum defended the records of President Bush and Defense Secretary Donald Rumsfeld while emphasizing his contention that the war in Iraq is but one front in a broader war against Islamic fascism. Mr. Casey maintained that the incumbent and the administration he supports were intent on a stay-the-course approach to the war that showed little promise of altering its difficult status quo.

Mr. Casey argued that, while in the Senate leadership, Mr. Santorum had presided over a ballooning of the deficit. Mr. Santorum countered that the Democrat had offered few specifics on budget alternatives, Social Security or overall federal spending.

The candidates frequently interrupted one another through the taping in NBC's Northwest Washington studio. Mr. Casey, belied his reputation as a somewhat stiff campaigner with an animated, often aggressive and seemingly relaxed performance. Mr. Santorum also looked for opportunities to go on the offensive, occasionally flashing irritation with his opponent.

The Republican's demeanor was more intense earlier in the debate, as the exchanges focused on Iraq and national security. The incumbent, from a position behind in the polls, had sought such forums for more than a year, but the session offered no obvious missteps by either opponent and no exchanges likely to be remembered as dramatic turning points in the race.

The program opened on a grace note with Mr. Santorum nodding his assent as Mr. Casey expressed condolences over the death of Mayor Bob O'Connor.

Pressed by the host, Tim Russert, on his position on the resolution authorizing the war in Iraq, Mr. Casey said he would have voted yes based on the information then available but would have voted against the war based on the information that has emerged since. Mr. Santorum said his view had not changed on the authorization vote, calling it, "a war of necessity."

Despite his apparent disagreement with that assessment, Mr. Casey said that the United States could not now abandon the mission in Iraq with an immediate withdrawal or a timetable for one. In yet another answer at odds with the views of his party's energetic anti-war wing, he said he would not vote to cut off funding for Iraq, nor would he vote for a set date, as advocated by Sen. John Kerry and other Democrats, for a withdrawal of troops.

"I don't think we can, Tim," he said to the NBC host. "I'm not ready to abandon this mission."

He said that the administration should fundamentally change its leadership and strategy, starting with the removal of Donald Rumsfeld as defense secretary.

Mr. Santorum disagreed, saying that Mr. Rumsfeld was "doing a fine job as defense secretary."

While emphasizing his willingness to disagree with the president, Mr. Santorum acknowledged, in response to a question from Mr. Russert, his consistently high level of voting support for the administration. "I think he's done a terrific job as president, absolutely," he said of President Bush.

As Mr. Russert continued to press the Republican on the situation in Iraq, Mr. Santorum, as he has throughout the campaign, tried to frame that conflict as a subset of a larger war against what he, and, increasingly, the administration have referred to as the war against Islamic fascism.

"We need to go out there and continue to fight this war on Islamic fascism," he said. "Not just, as my opponent likes to focus on, just the war in Iraq. That's a front of a multi-front war in which we're fighting against an enemy that's a very dangerous enemy."

Mr. Casey made light of that interpretation, suggesting that it focused on semantics rather than substance.

"After you get the terminology right, maybe you can have a seminar in Washington about whether bin Laden, whom we should be finding and killing, whether he's a dead terrorist or a dead fascist," Mr. Casey said. "And I think you should worry more about finding him and killing him."

But the Democrat offered one significant and somewhat surprising point of agreement with his opponent as he said that he would have voted for Mr. Santorum's proposal for a tougher policy toward Iran including economic sanctions and steps to encourage regime change in the Islamic republic. The Bush administration has opposed that measure in part because of a concern that its call for regime change would complicate efforts to talk Tehran away from efforts to develop nuclear weapons.

Turning to the budget, Mr. Russert pressed the challenger on how he could make the arithmetic work on his call for an end to deficits. Mr. Casey said he would raise taxes on Americans making more than $200,000 while rolling back part of the Bush administration cuts in the estate tax. Mr. Russert noted that such a change in income taxes would produce little more than a quarter of the revenue needed to bridge the budget gap while Mr. Santorum argued that the promises in the Democrat's campaign platform would in fact increase the deficit.

In response, Mr. Casey offered only a vague prescription for further savings, saying that the government could hire fewer consultants or close off-shore tax loopholes.

On Social Security, Mr. Casey criticized Mr. Santorum's advocacy of private accounts while characterizing the system's prospective deficits as a problem but not a crisis. He said that economic growth could address much of the system's problems, an answer greeted with apparent skepticism by Mr. Russert and scorn by Mr. Santorum.

"What you heard from Mr. Casey is what you hear all the time. No specifics. No answer," Mr. Santorum said. "He gave absolutely -- he didn't give you one program that he would cut. Not one. And he won't. And he won't give you an, he won't give you an answer on Social Security. He won't give you an answer on anything to make any changes."

Mr. Santorum was on the defensive on an oft-quoted statement in his first Senate campaign in which he urged an increase in Social Security retirement ages. As he has in the past, the Republican said he no longer holds that view, and that he now feels that personal accounts could bring a solution without reducing benefits.

Mr. Casey argued that that approach would only weaken the system.

While both candidates hold generally conservative views on abortion, they showed a sharp disagreement on the federal government's recent decision to allow over-the-counter sales of the so-called Plan B morning-after pill.

Endorsing the decision, Mr. Casey said, "It is contraception, and I support it, and it's a difference of opinion."

Mr. Santorum called the pill dangerous, arguing that, "if the egg has been fertilized ... and the pill is taken, it does cause an abortion. It's inconsistent with his previous position. It's a classic attempt of him, how in a general election, to try and middle and, and, and violate his principles."

Referring to Mr. Casey's father, the late governor known for his anti-abortion views, Mr. Santorum added, "I think his father would be very upset if, if he were alive today and, and heard him be supportive of something like this."

Asked about that statement in the studio afterwards, Mr. Casey said, "The last thing we need is a lecture from Mr. Santorum about my father."