For the first time since terrorists turned him into a war president 16 months ago, George W. Bush on Tuesday night will address a nation that has serious questions about his leadership.

He must convince the American public of the urgency of attacking Iraq when support is falling for such a venture and for his foreign policy generally. He must demonstrate concern for the economy when Americans are worried he is not doing enough -- and is selling a tax cut opposed by a majority of the public and key lawmakers in his own party. In addition, he must also persuade lawmakers to make good on his big domestic promises, including a Medicare overhaul fraught with political risk.

Less than three months after spearheading a historic midterm election victory for the Republicans, Bush looks embattled rather than triumphant. On the two biggest issues of any presidency -- national security and the economy -- the public has far more doubts about him today than it did just a few months ago. As such, Bush arrives for his State of the Union message, his fourth address to Congress, suddenly under pressure.

"They've got big, tough issues," Republican pollster Robert Teeter said of the White House. Bush "is in a situation where you've got a lot of important balls in the air" and a public that is "at a minimum, uncertain" about the future. Teeter said polls showing a decline in Bush's approval rating -- from the mid-80 percent range to the mid-50 percent range, where he was before the Sept. 11, 2001, attacks -- are no cause for panic, but "will focus their attention" in the West Wing.

A poll last week by the nonpartisan Pew Research Center for the People and the Press found that 87 percent of Americans believe this year's State of the Union address is as or more important than last year's speech, as doubts about international and economic policies have risen. By nearly 2 to 1, Americans said Bush could be doing more to boost the economy, a sharp increase from a year ago.

Meanwhile, a flurry of polls conducted this week by The Washington Post and other news organizations found only bare majorities supporting Bush on foreign policy -- an area where he commanded support of more than 80 percent a year ago.

"The agenda in 2003 is not united, the public is not united and the public is much less confident of his leadership this year than they were a year ago," said Peter Hart, a Democratic pollster. "His personal challenge is to reestablish a sense of presence and leadership that seems to have been lost."

Bush's speech will thoroughly address matters domestic and economic; he'll push for Medicare legislation and his "compassion agenda," in addition to his $670 billion tax cut. But political strategists and White House officials agree that Iraq will inevitably be the subject of dominant interest -- and the most urgent test of Bush's leadership.

Because of the administration's steady vows to disarm or oust Iraqi President Saddam Hussein and the massing of U.S. troops in the Persian Gulf region, Bush has all but committed the country to war. Yet allies are balking and the American public is unhappy about acting alone and denying U.N. inspectors the additional time they seek.

Republicans on Capitol Hill, a few of whom have uncharacteristically begun to question Bush's policies, agree that Bush must deliver "a galvanizing speech" Tuesday. "This is the first crisis of confidence in his leadership since September 11th," said a prominent GOP Senate aide. "This is the speech that redirects the country's attention to the need to go to war at a time when he's at a nadir in his foreign policy leadership."

On Iraq, Bush's challenge is particularly delicate. Americans are still generally supportive of ousting Hussein, and there would almost certainly be a vast increase in support for Bush and the attack once it begins. But Bush is not ready to order war -- in part because U.N. deliberations are ongoing, Turkey has not yet committed to cooperate, and British Prime Minister Tony Blair, with whom Bush promised to consult, has not arrived in Washington for such talks.

"What needs to be done at this point to pull things together is the president has to be decisive, saying, 'This is it; no more fooling around; I've made a decision,' " said Gary Schmitt, a former Reagan administration official who heads the Project for the New American Century. "The problem is he doesn't want to do this before he's consulted with Blair, because he wants to make Blair a partner, not a poodle."

Therefore, Schmitt said, Bush is in the awkward position of making the case that Hussein is a bad man -- something Americans already believe -- without stating what must be done. "The problem with presidential rhetoric is sooner or later, the coin gets spent," he said. "You can only make so many speeches on the same subject, and people stop listening."

White House communications director Dan Bartlett said Bush views Tuesday's speech as an "opportunity to educate the public and the world about the threat that Saddam Hussein poses." While asserting that "we are entering the last phase," Bartlett warned: "Don't expect any declaration of war in this speech because of where we are in the diplomatic phase."

Bush allies cautioned against expecting new details of the case against Iraq. "I don't think he will get as much into Iraq as people expect; I think it will be general, and you'll get more specifics later," said GOP lobbyist Charlie Black, who is close to the White House. Rather, Black said, Bush will link Iraq and his foreign policy more closely with homeland security. "It's all under a big umbrella theme," he said.

Bush's address will deal with North Korea and Iran, the other countries he put in the "axis of evil" a year ago. But the Iraq component is more urgent, intended to amplify the administration's rhetoric, which has begun to escalate.

National security adviser Condoleezza Rice said last week that Hussein has responded with "a clear and resounding no" to disarmament, and she warned that "time is running out." A day later, Deputy Defense Secretary Paul D. Wolfowitz echoed the warning. Even Secretary of State Colin L. Powell, ambushed at the United Nations by the French opposition to an attack, dropped his enthusiasm for arms inspections.

Both critics and supporters of the president said they believe that, at least in the short term, Bush should be able to rally the country behind his Iraq policy, as he did in September with his speech to the United Nations after several weeks when the administration was on the defensive. "I think the temporary dip will fade starting [this] week when the president commands center stage," said Scott Reed, a Republican strategist.

But whether that support proves durable over the long run is another matter. If Americans do not fully embrace the cause, then support could slip easily, particularly if the war went slowly and casualties were high. Bush is in a much more fragile position than he was in rallying the nation to war against Afghanistan, where the moral case was clear, the national interest certain, and bipartisan agreement easy. Americans are wondering not only why the country must go to war now, but also what the long-term risks and commitments will be. On this, Bush has been quiet.

Eric V. Larson, who studies public opinion and war at the Rand research group, said long-term support for the war would depend on Americans' perception of the importance of the mission, the prospects for success, the likely costs and casualties and the support for the war from national leaders. Support for war in Iraq, he said, will depend on a key question: "Do all parties come together and say this is worth doing, or do they divide along partisan lines?"

Last fall, Bush found it easy to get bipartisan support, because he coupled action against Hussein with a willingness to let the United Nations resume arms inspections -- and he shifted his goal from "regime change" to the more modest "disarmament." Now, though, he must demonstrate why he may go to war with only a few allies on board and possibly without a fresh authorization from the United Nations.

James Steinberg, deputy national security adviser in the Clinton administration, said the president has failed to answer many of the key questions: why he believes the United States should go to war; what Hussein could do to avert war; how important it is if key allies oppose a war; and what the United States would have to do in Iraq after a war. Some believe Bush should also brace the nation for the street fighting that could occur if the campaign did not succeed quickly.

And Bush may not be able to make an open-and-shut case that Hussein has weapons of mass destruction. "You'll never come up with enough information to convince everybody," said Kenneth Adelman, a former Reagan official who is on a Pentagon advisory panel. He acknowledged that "the momentum has gone away from the administration," but he said Bush can quickly regain his advantage by convincing Americans "that time is not on our side."

Though a temporary boost in support for military action and the commander in chief will come easily enough, Bush has much work to do, starting Tuesday, to establish more durable support for his foreign policy and for his leadership generally. "The war on terrorism, like World War II, was a war you felt in your gut had to be fought," a former government official said. "People may feel this [the need to oust Hussein] in their head, but they don't feel it in their gut."

President Bush faces faltering support on Iraq and the economy.President Bush discusses his State of the Union address with, from left, speechwriters Matthew Scully, John McConnell and Michael Gerson in the Oval Office. Bush will speak before Congress and television cameras Tuesday.