President Bush said last night that Secretary of State Colin L. Powell will brief members of the U.N. Security Council next week on evidence showing that Iraq possesses, and is still engaged in producing, weapons of mass destruction, signaling the start of an intensive campaign to win over international and domestic opinion.

In his address to the nation, Bush said he will ask the Security Council to convene a special meeting next Wednesday so that Powell can "present information and intelligence about Iraq's illegal weapons programs, its attempts to hide those weapons from inspectors and its links to terrorist groups." Bush, who last night began to catalogue some of that evidence, also repeatedly referred to the missing weapons materials cited on Monday by the chief U.N. weapons inspector in an unexpectedly tough report.

Despite a transatlantic breach last week over the administration's war plans -- and opinion polls showing deep disapproval overseas of Bush's Iraq policy -- administration officials said they feel their case for military action was strengthened by the U.N. report of Swedish diplomat Hans Blix. But Bush's decision to send Powell to New York is also an acknowledgment that the administration believes it must do more to convince Security Council members of its position and to ensure the widest possible international backing if the president decides to go to war.

White House spokesman Ari Fleischer said yesterday that a new Security Council resolution authorizing the use of force would be "desirable, but it is not mandatory," adding that insufficient support for a new resolution would not stop the United States from acting alone. Fleischer's comments reflected the administration's delicate balancing act of seeking international backing while keeping its options open to maintain pressure on Iraqi President Saddam Hussein.

Administration officials said no decisions have been made on the content of a new resolution, including the final deadline for Iraq's compliance, but they said there is little patience for a protracted negotiation with other Security Council members. Officials believe tacit council support for a military strike -- or at least opposition that is not active -- is possible.

According to U.S. and diplomatic sources, the options include an early resolution authorizing the use of force, which appears unlikely; an agreement to set a deadline for Iraqi compliance after council members agree that force is necessary; or an agreement to set a deadline, after which all member countries would be free to make their own decisions.

Administration officials said Bush will take an active role in the days ahead in seeking to achieve an agreement, on the assumption that it would be difficult for foreign leaders to turn down a direct appeal from the president.

In one sign of diplomatic movement yesterday, Russian President Vladimir Putin said that Russia, which has pushed for a peaceful solution, "may change its position" if Iraq continues to hamper U.N. weapons inspectors. "We intend to work with other Security Council members, including the United States, to work out other decisions -- I won't say what kind, but tougher than the existing decisions," Putin said in Kiev, the capital of Ukraine.

Russia has veto power and has been closely aligned with France, another permanent Security Council member that is skeptical about an immediate decision to go to war. Administration officials said they considered Putin's statement to be a significant shift in tone.

French officials have made a public show of opposition to war. But even French officials, speaking privately, acknowledge that mid-March is the outside limit for when the United States could launch an invasion of Iraq because of the warming temperatures in the Persian Gulf region. U.S. officials believe that French support is possible if it appears France has won concessions on extending the inspections for even a limited amount of time.

Sen. Joseph R. Biden Jr. (Del.), the senior Democrat on the Foreign Relations Committee, told reporters yesterday that the administration has evidence on Iraq's weapons programs "that can change people's minds." He described it as "enough circumstantial evidence that if there were a jury trial I could convict you."

Citing intelligence sources, Bush last night charged that Iraq has thousands of Iraqi security personnel hiding documents and materials from U.N. inspectors, that Iraqi intelligence officers are posing as scientists and that scientists who cooperate have been threatened with death.

In a speech on the Senate floor earlier in the day, Biden warned Bush that he has not yet made an effective case to the American people and to the world for why military action is needed now. Last weekend, at an international forum in Switzerland, Biden noted, "I found myself confronted with the most uniform and significant anti-American sentiment that I've ever encountered in my career of 30 years dealing with foreign leaders abroad."

Biden urged Bush to "lower the rhetoric," saying the United States "should not appear to be the petulant nation wondering why the rest of the recalcitrant world will not act with us, showing our impatience." He said that the administration should give the inspectors more time and should work to build domestic support, in part by making clear the uncertainties of war and occupation. He estimated that 75,000 U.S. soldiers would need to remain in Iraq at least 11/2 to five years after an invasion.

Today, Powell and Defense Secretary Donald H. Rumsfeld will brief House members on Iraq, and officials said more evidence will be declassified in the coming weeks.

Both Bush and Powell will speak with foreign officials this week in an effort to reach an agreement at the Security Council, culminating in a crucial meeting at Camp David on Friday with British Prime Minister Tony Blair.

"All of this now is about waiting for Tony Blair," said one administration official. "The meeting at Camp David is incredibly important for what happens next."

A senior State Department official noted that U.S. officials spent a week negotiating with British officials on the Security Council resolution authorizing the weapons inspections in November before attempting to win support from other council members. "We know if we don't have the Brits, we don't have anybody," he said.

Last weekend, Blair said inspectors "should have whatever time they need," but that the process should not take months. He added that he could foresee military action without a second resolution only if such a resolution were vetoed despite a clear report from inspectors that Iraq was not cooperating.

In London, yesterday, British Foreign Secretary Jack Straw for the first time declared Iraq in "material breach" -- or violation -- of the November resolution, citing what he called the "damning and disturbing" report by weapons inspectors. The Bush administration made such a declaration in December, but no other Security Council member had followed suit until now.

As part of the run-up to Blair's visit, Bush spoke on Monday with Spanish Prime Minister Jose Maria Aznar -- a conservative who has forged strong ties with Bush. The president will welcome at the White House on Thursday Italian Prime Minister Silvio Berlusconi, another conservative.

Powell spoke to Straw yesterday and will meet with Pakistani Foreign Minister Khurshid Mahmud Kasuri at the State Department today. Both Spain and Pakistan have seats on the Security Council.

One administration official said the United States is making the case to its allies that this is not only a test of Iraqi compliance, but also a test of the United Nations' "willingness to be relevant." Pointing to the resolution approved unanimously nearly three months ago, he said: "That was the midterm test. This [the coming debate] is the big test because we are on the edge."

Officials continue to express hope that, in the meantime, the inspections will turn up incriminating evidence of Iraq's weapons programs.

The administration believes Iraq has been thwarting inspections by removing materials before inspectors arrive, but a more aggressive use of helicopters will seek to block those efforts. The helicopters will arrive at sites before inspectors and their Iraqi minders can, and they will survey the surrounding area to prevent any removal of materials.