KENNEBUNKPORT, MAINE, AUG. 28 -- As the crisis in the Persian Gulf drags on, President Bush is facing growing pressure to explain more clearly the reason for the largest U.S. military deployment since the Vietnam War.

Is it to defend Saudi Arabia from Iraqi attack? Is it to ensure cheap oil for the United States and other industrialized nations? Is it to restore a monarchy to Kuwait? Is it to repulse the greatest threat to the civilized world since Adolf Hitler?

In the weeks since Iraqi troops invaded Kuwait, Bush has offered all of those rationales for his Persian Gulf policy.

Bush won bipartisan support from congressional leaders in Washington today when he reiterated his near-term goals of deterring Iraqi aggression against Saudi Arabia and using the international embargo to force Iraq to withdraw from Kuwait. However, lawmakers also told Bush that he needs to go further in explaining the rationale and objectives for his actions to the American people. Some of them cautioned Bush that it will be more difficult to sustain public support in the months ahead without such an explanation.

House Majority Leader Richard A. Gephardt (D-Mo.) said, "One of the suggestions made was the importance of the president talking directly to the American people soon to try to articulate these goals so they know what we are trying to do and what is in America's vital interests, what is in the world's vital interest. . . . "

The month-old crisis has shown two dimensions of the Bush presidency. One is the self-confident, behind-the-scenes diplomat, dialing world leaders to rally support for a worldwide condemnation of the invasion and pushing the United Nations to demand the unconditional withdrawal of Iraqi President Saddam Hussein's army.

That skillful diplomacy has helped Bush earn overwhelming support for his initial steps in countering the Iraqi invasion. But Bush's public explanations of the reasons behind the countermoves he has ordered have been less consistent, leading to calls for a clearer explanation of the U.S. mission.

A few days ago, Sen. Bob Kerrey (D-Neb.) warned that Bush will soon have to tell the American people why he is risking the lives of U.S. troops. "Part of the problem is, in fact, at the first post-Cold War moment when we're putting Americans in harm's way, we aren't, it seems to me, being provided a sufficient amount of information to really engage meaningfully in a debate about whether or not this is appropriate," Kerrey said on NBC's "Meet the Press."

The only legitimate reason for the deployment, Kerrey said, was to defend the Saudis from Iraqi attack. But he questioned the rationale "that says we're going to go there and have our young people die so that we can have cheap oil here at home."

Sen. Joseph R. Biden Jr. (D-Del.), speaking Monday on NBC's "Today Show," predicted that Bush will continue to enjoy strong popular support for his gulf policy "if he clearly defines what his strategic purpose is. . . . We have to hear from the president what his strategic requirements are for the region, what he, long term and short term, sees our interests to be in the area."

Public opinion polls underscore the reservations expressed by the two Democratic senators. A Wall Street Journal-NBC News poll released last week showed overwhelming support for military action if Iraqi troops attack Saudi Arabia, but far less support for military action to keep oil prices low.

In the poll, 74 percent of those surveyed said they would favor a military response to an attack on the Saudis, but only 27 percent said they approved of military action to prevent gasoline prices in the United States from reaching $2. Only 39 percent said military force was justified to prevent an oil-induced recession in this country.

Administration officials argue that Bush's goals have not changed since the onset of the crisis. He wants the immediate and unconditional withdrawal of Iraqi troops from Kuwait; the restoration of the Kuwaiti government; the release of Americans and other foreign nationals now held hostage by Iraq, and long-term stability and security in the gulf region.

But the president's attempts to articulate his reasons for deploying U.S. troops have been less concise and consistent.

On Aug. 8, when he announced the deployment, he told the American people he had done so "to assist the Saudi Arabian government in the defense of its homeland."

A week later, speaking to Pentagon employees in Washington, he warned that preservation of the Middle East's energy resources were "truly vital" and thus worth fighting for. "Our jobs, our way of life, our own freedom and the freedom of friendly countries around the world would all suffer if control of the world's great oil reserves fell into the hands of that one man, Saddam Hussein," Bush said.

But on Aug. 20, in speeches to the Veterans of Foreign Wars convention in Baltimore and a political fund-raiser in Rhode Island, Bush dropped the energy rationale, concentrating instead on the demonization of Saddam as a modern-day Hitler, the personification of "fundamental evil." Bush's justification for his policy hinged more on arresting aggression, in contrast, he said, to the world's failure to confront Hitler in the days leading up to World War II.

When he gave those speeches, Bush was furious over the hostages. He ordered aides to toughen the speeches and when he still wasn't satisfied he personally rewrote parts of one of them as he flew from Washington to Rhode Island.

Outside experts interpreted those speeches as Bush's effort to prepare the American public for military conflict. But administration officials privately played down the personal attacks, suggesting they were designed to undercut Saddam's support in the Arab world, which the Iraqi leader is courting furiously.

But Bush's personal attacks on Saddam may have a price. Having equated the Iraqi president with Hitler, it will now be more difficult to seek or accept a diplomatic solution that keeps him in power.

Moreover, the president's shifting rhetoric appears to have left the American public slightly confused. A Newsweek poll released this week shows overwhelming support for Bush's stated goals in the conflict. It also found that roughly three-quarters of Americans support destruction of Iraq's chemical weapons capability and its potential nuclear capability. Roughly the same percentage supported removing Saddam from power.

But 80 percent also said the United States should wait for the economic sanctions to take effect rather than initiating military action.

Last week, White House Chief of Staff John H. Sununu, testily defending Bush from criticism that he should not be on vacation during the crisis, said, "This is not a public relations administration. This is a do administration, and the president does it quite well."

That reflects a deeply held view within the administration that Bush will be judged on the results of his actions.

Administration officials suggest that nothing less than a new world order is at stake in the crisis, as the superpower conflict of the last four decades gives way to a less certain balance of power, and that this justifies the U.S. commitment. The conflict in the gulf, they believe, may be the defining moment of this new order.

But it has been many years since an American president committed so many troops so far away with such an uncertain outcome. The pressures to justify their presence there -- whether called public relations or simple communication -- are certain to increase with time.

Balz reported from Kennebunkport, Hoffman from Washington. Staff researcher Bruce D. Brown contributed to this report.