His skin has turned pale, and his hair looks thinner and grayer. He seems to be constantly fighting a cold. His tailored suit coats seem to hang from a trim frame turned gaunt. He is working, he says, "night and day."

As he struggles against the clock to piece together a majority for a new U.N. Security Council resolution on Iraq, British Prime Minister Tony Blair looks and sounds like a man under siege. America's staunchest ally is paying a stiff price for his support.

Already this week, one cabinet minister has publicly called his Iraq policy "reckless" and threatened to resign, and another is reported to be "considering his position" if the United States and Britain take military action without a new U.N. resolution authorizing it.

Rebels in his ruling Labor Party today demanded that he step down. And a new poll for the Times of London newspaper found that only 19 percent of Britons responding would support military action without a new resolution.

"Seeing him on television, he has the look of someone who feels that events are starting to get out of control," said Raymond Seitz, a former U.S. ambassador to London. "You have to be terribly worried that we could possibly lose a close and valued ally because of his relationship with the United States."

Blair and his supporters insist that he can weather the storm, and many political analysts agree. While Blair's general approval ratings are down as well, no coherent opposition to his leadership has emerged, either in his own party or in the rival Conservative Party.

The prime minister is meeting daily with world leaders and working the phones. He declares that he has not given up on the new resolution to authorize war against the government of Iraqi President Saddam Hussein, even after the leaders of France and Russia said they would veto any new measure.

"Let us not be under any illusion," he told reporters this morning, after meeting with Portuguese Prime Minister Jose Manuel Durao Barroso. "The only reason we made any progress at all in the past few weeks has been because of the threat of force. And my concern is that if countries talk about using a veto in all sets of circumstances, the message that sends to Saddam is, 'You are off the hook.' "

At times, Blair seems isolated from his allies as well as his enemies. He has spoken to President Bush by phone twice in the past week, aides said, and has won Bush's support for seeking the second resolution. But administration officials have said the United States does not need another resolution and is allowing the process to go forward largely as a political favor to Blair.

On Sunday night, Clare Short, the cabinet secretary for international development, told a BBC radio program she would quit if Blair went to war without U.N. approval. "I will not uphold a breach of international law, or this undermining of the U.N.," said Short, a popular member of the Labor Party's left wing.

Newspaper reports added that former foreign secretary Robin Cook, who holds cabinet rank as leader of the House of Commons, might also step down in event of war. Cook has not commented.

Blair resisted calls from loyalists to fire Short, while other cabinet members rallied to support the prime minister and criticize Short for going public. Asked to comment, Blair said: "I'm working flat-out for a second resolution, and the important thing at the moment is that we stay together."

Antiwar activists in Labor have called for an immediate vote in Parliament if war breaks out, and Blair has promised he would allow a debate and vote. Political analysts predict he would win even if he suffers a large-scale defection from his party, because the Conservatives have pledged to support his position on Iraq.

If the ensuing war is short, sharp and successful, Blair's supporters contend, he will emerge unscathed and perhaps even strengthened. If not, said Robert Worcester, chairman of the MORI polling organization here, "All bets are off."

One problem, Worcester said, is that antiwar stalwarts in Labor are being joined by lawmakers who are fed up with Blair for other reasons. Some did not get positions in government, while others disagree with his domestic policies or simply resent the Teflon quality of a politically moderate Labor prime minister who has won two landslide electoral victories while departing from many of the party's traditional policies.

"There are an awful lot of people waiting to get even," Worcester said.

Unlike Bush, who tends to confine his meetings to supporters of his Iraq policy, Blair has made a point of publicly engaging with opponents. Monday night, he was grilled for an hour on Independent Television here by 20 women opposed to war. He seemed to win grudging respect from some in the audience, but a handful of the participants slow-clapped him at the end as a sign of disapproval.

British Prime Minister Tony Blair and his supporters insist he can weather the storm, and many analysts agree.