he two top American military and diplomatic officials in Iraq conceded Tuesday that the Bush administration’s overall strategy in Iraq would remain largely unchanged after the temporary increase in American forces is over next summer, and made clear their view that the United States would need a major troop presence in Iraq for years to come.

Facing a day of withering questions from two Senate committees, Gen. David H. Petraeus and Ryan C. Crocker, the American ambassador to Iraq, were unable to argue that the heightened troop levels had made more than fragile and transitory progress. Nor could they reassure senators that American efforts could help forge political compromise among battling sectarian groups.

The clashes over war strategy were more intense and emotional than had unfolded during the previous day in the House, reflecting the powerful passions and ambitions of a Senate that includes five presidential aspirants. Some exchanges in the Hart Senate Office Building on Tuesday struck a tone not heard on Capitol Hill in 40 years, since Gen. William C. Westmoreland defended the American approach to defeating North Vietnam.

In responding to General Petraeus’s recommendations, the White House said President Bush would address the nation at 9 p.m. on Thursday. He is expected to endorse the call for no more than a gradual troop reduction in coming months, one that would leave some 130,000 American troops in Iraq by next summer.

But Democratic leaders issued a pre-emptive attack on that approach, with Speaker Nancy Pelosi emerging from a White House meeting to denounce the president’s approach as “an insult to the intelligence of the American people.”

As General Petraeus and Ambassador Crocker wound up two days of grueling testimony to the House and Senate, Ms. Pelosi said everything she had heard “sounds to me like a 10-year, at least, commitment to an open-ended presence and war.”

Democrats who were briefed on the White House meeting said that Ms. Pelosi had told Mr. Bush that much of the public would be shocked at the prospect of an undefined, long-term presence in Iraq. They said the president had acknowledged that he foresaw an extended involvement in Iraq and was backed by Senator Mitch McConnell of Kentucky, the Republican leader, who said the nation had made a commitment to the region.

The recommendation by General Petraeus calls for the step-by-step withdrawal between now and next July of the 30,000 additional troops that Mr. Bush has sent to Iraq as part of what has been called a “surge” in forces, which he announced in January. But that leaves open the question that permeated the heated discussions in the Senate on Tuesday, about whether keeping the remaining 130,000 troops would serve a purpose.

“Buy time?” asked an angry Senator Chuck Hagel, Republican of Nebraska, who announced Monday he would retire from the Senate next year. “For what?”

General Petraeus, pressed first by Senator Susan Collins, a Maine Republican who is under tremendous pressure to abandon her lukewarm support for Mr. Bush’s war strategy, and then by Senator Hillary Rodham Clinton of New York, conceded that he would be “hard-pressed” to justify America’s presence in Iraq if there is no political progress in Iraq over the next year.

Senator John W. Warner, Republican of Virginia, who is one of the party’s leading voices on foreign policy, asked whether the current strategy in Iraq was “making America safer.” General Petraeus retreated to an explanation that he was doing his best “to achieve our objectives in Iraq.”

But when pressed again, he said: “Sir, I don’t know, actually.”

The general and the ambassador, who in the past have talked expansively about the regional and global effects of the Iraq war, stayed narrowly in their lanes of expertise on Wednesday, and stepped around repeated questions about whether a series of tactical victories in Anbar Province or some neighborhoods of Baghdad could be transferred into a broader agreement that would end a state of civil war.

Nor would they be drawn into any estimates of how many more years a major American troop presence would be required — or even when the oft-promised training of Iraqi troops would be complete enough to allow Americans to step into the background.

“I’m as frustrated with the situation as anybody else,” an exasperated-sounding General Petraeus said in a particularly pointed exchange with Senator Robert Menendez, Democrat of New Jersey. Briefly breaking out of the flat tone in which he has delivered his analyses of troop strength and the reliability of Sunni tribes who have turned against Al Qaeda, General Petraeus said, “This is going on three years for me, on top of a year deployment to Bosnia, as well, so my family also knows something about sacrifice.”

By the end of two days of testimony, it appeared clear that the Democrats still did not have enough votes to cut off funding for the war or set deadlines for an American withdrawal.

It was also clear that, unless Mr. Bush includes a surprise in his Thursday speech, the strategy for the remaining troops will be a familiar one. The planned level of about 130,000 troops by next July is about the same level as was in Iraq in February. When asked about changes in the troops’ mission, General Petraeus said their approach would be only “slightly modified.”

But it was also clear that many of the key Republicans whom the White House needs to keep on their side no longer believe that President Bush has a workable strategy. They questioned whether any number of months, and any tactical alliances with moderate Sunnis or Shiites, would bring the government of Prime Minister Nuri Kamal al-Maliki closer to the national reconciliation that Mr. Bush said in January would be spurred along by the larger American presence.

Sen. Joe Biden challenged the top U.S. officials in Iraq during a Senate hearing on Tuesday, saying the country is no closer to a lasting political settlement than when the military began increasing troop levels there eight months ago.

Biden also told Army Gen. David Petraeus, commander of U.S. forces in Iraq, and Ryan Crocker, U.S. ambassador to Iraq, that there's no evidence Iraq's warring factions will start governing together if the U.S. military continues with its "surge."

"We should stop the surge and start bringing our troops home," he said at Tuesday's hearing before the Senate Foreign Relations Committee, which he chairs. "We should end a political strategy in Iraq that cannot succeed and begin one that can."

Petraeus and Crocker encountered similar frustration from other senators, including Republicans, during a day of intense testimony before Biden's panel and the Senate Armed Services Committee.

"Are we going to continue to invest American blood and treasure at the same rate we are doing now? For what?" asked Sen. Chuck Hagel, R-Neb., who recently announced his retirement. "The president said, 'Let's buy time.' Buy time? For what?"

Petraeus testified that the success of the ongoing troop surge in Iraq had prompted him to recommend modest troop reductions over the next several months and cuts of as many as 30,000 by next summer. President Bush is expected to endorse the redeployment plan this week, according to published reports.

But many Democrats want much larger reductions than Petraeus cited and are hoping to win moderate Republican support for legislation this fall that would at least begin substantial troop cuts by year's end. Formal debate on Iraq could start as early as next week.

Both Petraeus and Crocker warned that leaving Iraq unstable would be disastrous, allowing Iran to establish regional hegemony and al-Qaida in Iraq to bounce back from defeats this summer at the hands of U.S. and Iraqi forces.

The testimony by Petraeus and Crocker comes on the heels of several major war analyses -- by government agencies and an independent commission -- all highly critical of the situation in Iraq.

Biden, a Democratic candidate for president, noted differences between Petraeus' assessment of declining violence in Iraq and the less optimistic assessment from the General Accountability Office, Congress' nonpartisan investigative arm. The GAO said recently that levels of violence remained high.

Petraeus explained that his information was more up to date. The GAO's cutoff date for information was at least five weeks earlier.

"I don't want to get in an argument about that, but if you look at your own chart, there have been at least four other occasions where there have been significant decreases in violence over a three-month period and then it shot back up," said Biden, who made his eighth trip to Iraq last week. "Five weeks in Iraq is a moment, as you know better than I do, general."

Earlier, Biden said the debate over whether violence is decreasing in Iraq "in a sense misses the point" and that lasting stability requires a political settlement among the warring factions.

Biden said the surge of nearly 30,000 troops serves a "fundamentally flawed strategy" of helping Iraqis build a strong national unity government in Baghdad. He said that won't happen "in the lifetime of any of us."

Making the same pitch he's made for more than a year, he said it would make more sense to give the Iraqi warring factions breathing room in their own regions with a limited central government in charge of common concerns, such as distribution of oil revenues.

"Without a settlement, the surge is [at] best a stopgap that delays but will not prevent chaos," he said. "Its net effect will be to put more American lives at risk, in my view, with very little prospect of success."