WASHINGTON -- Sen. Edward M. Kennedy led Democrats Friday in a spirited attack on President Bush's Iraq policy, reflecting growing frustration about their inability to restrain the president's drive toward military confrontation with Saddam Hussein.

In a nationally televised speech at Johns Hopkins University's School of Advanced International Studies in Washington, Kennedy said Bush "has not made a convincing case that we face such an imminent threat to our national security that a unilateral, pre-emptive American strike and an immediate war are necessary."

Conceding that the Iraqi president is a "tyrant" and his regime presents "a serious danger," the Massachusetts Democrat nonetheless argued that Bush should give United Nations weapons inspectors a chance to disarm Iraq before resorting to war. He commended Bush for inviting the United Nations to act, but argued that the president must give it time to do so. He said the U.N. Security Council should authorize force if the inspections failed, at which point the United States would be prepared to act.

Kennedy's speech, carried live on cable TV networks, was the most comprehensive argument leveled against Bush's policy by a top Democratic lawmaker since the administration began rattling sabers this summer. France is making essentially the same argument at the U.N. Security Council, as are many other U.S. allies.

Yet while Kennedy's views are strongly shared among many Democrats, they are not likely to prevail in Congress, where election-year politics and dread of another Sept. 11-like terrorist attack have forged bipartisan support behind Bush's aggressive stance.

The president is pushing Congress to approve a resolution giving him a green light to wage war to stop Saddam from developing or using weapons of mass destruction. Lawmakers are negotiating with the White House over precise wording, but Congress is likely to give Bush the authority he seeks.

During a political stop Friday in Colorado, the president said he was "willing to give peace a chance," but he continued to threaten military action. He prodded the United Nations to approve a tough resolution demanding Iraq's disarmament.

'Now's the time'

"I want the United Nations to work. I want him to do what he said he would do. But for the sake of our future, now's the time," Bush said. "We must make sure this madman never has the capacity to hurt us with a nuclear weapon or to use the stockpiles of anthrax that we know he has."

But it was Kennedy's high-profile speech that energized the debate Friday. Republicans promptly attacked him, accusing him of minimizing Saddam's threat and of making the United States subservient to the United Nations.

"Sen. Kennedy offered the most thorough and cohesive argument for complacency so far," said Rep. Tom DeLay of Texas, the third-ranking Republican leader in the House of Representatives. "Subcontracting our national security to the United Nations, as Senator Kennedy recommends, would be a foolish blunder."

Senate Republican leader Trent Lott, R-Miss., said Kennedy's call for a U.N. authorization of force "sounds like a series of hurdles."

"The United States is not going to just stand still, stand mute and allow this issue to continue to fester and become a greater and greater threat to all of us," Lott said.

In his speech, Kennedy argued that Bush's shift of focus to Iraq is weakening America's war on terrorism and risks alienating allies that are needed in that cause. He said al-Qaida, not Iraq, remained the nation's most urgent menace. He said that if Bush pursued war without working first through the United Nations, he risked inflaming the Arab world and fomenting more terrorism. Kennedy warned that a cornered Saddam might attack Israel, which has pledged to retaliate, possibly with nuclear weapons, risking a regional war with world-shaking consequences.

And the younger brother of former President John F. Kennedy recalled "an autumn of danger four decades ago, when missiles were discovered in Cuba, missiles more threatening to us than anything Saddam has today." In October 1962, President Kennedy resisted advice from his top military advisers to attack those Soviet missiles in Cuba unilaterally. He took America's case to the United Nations, won global support, imposed a naval embargo around Cuba, forced Moscow to dismantle the missiles and averted war. Just as JFK did then, his brother concluded, "in 2002, we too can and must be both resolute and measured."

But the president appears to have the support he needs to prevail in Congress. With rare exceptions, Republicans are solidly behind him. And many moderate Democrats share his conviction that Saddam represents an imminent threat. Some of those Democrats face close elections in November and already have been targeted by Republicans as soft on terrorism.

Another source of friction within Democratic ranks is a desire by some lawmakers to vote swiftly on an Iraq resolution to get the issue behind them so they can campaign for election on economic issues. Others want to delay the vote beyond the Nov. 5 elections, but Bush opposes that.

Senate Majority Leader Tom Daschle, D-S.D., reflected the tension Thursday when he said the latest proposed resolution still needed significant changes, but that he would bring the resolution up for debate early next week.

Asked this week why he wouldn't delay the vote until after Nov. 5, Daschle said: "That would extend the debate for six weeks. That would extend the debate for two months. I mean, that's exactly what I think some would prefer that we do -- that we just do nothing but all Iraq, all the time."