WASHINGTON - After countless phone calls to world capitals and hours spent convincing international leaders about the seriousness of the Iraqi threat, Secretary of State Colin L. Powell went to sleep Thursday night thinking he might have come up short.

Powell had tried hard. Over a period of weeks, he was at times glued to his cell phone. Even at his daughter's wedding Nov. 3, Powell was on the phone with the French foreign minister, putting final touches on an important breakthrough. Then he turned off the phone - to walk his daughter down the aisle.

Powell wanted to deliver his dream goal to President Bush: a unanimous vote in the United Nations Security Council threatening war against Iraq if Saddam Hussein refused to disarm.

But on Thursday evening, a key member of the Security Council, Russia, was still wavering about whether to support a tough new U.N. resolution. Syria, an Iraq ally, wasn't on board, either.

Given the nagging uncertainty, it's easy to imagine why Bush appeared relieved as he smiled with Powell in the Oval Office yesterday morning. It was just moments after the Security Council voted 15-0 to approve the tough resolution that Bush had been calling for.

The vote capped seven weeks of intense diplomacy and deal-making led by Powell. The United States hoped the world could send a clear message to Hussein that he must act immediately or face "serious consequences" - in all likelihood, war.

The U.N. vote was a historic display of world unity, and senior administration officials offered a glimpse into the late-stage diplomacy that led to it.

"This at some times became an excruciatingly difficult task as we first put the British into the basket with us and then slowly all of the others," one senior official said. "We were interested in getting as many votes as we could for the resolution."

As of several weeks ago, two Security Council nations, France and Russia, who have veto power over resolutions, were concerned that the United States was seeking language that would automatically trigger war if Hussein ignored demands to disarm. Analysts held out little hope that Syria, representing the Arab world on the council, would back a resolution.

French officials pressed for more U.N. control over how to respond to Iraqi defiance. They wanted the Security Council to reconvene after any such defiance to determine whether Iraq had violated the new resolution before military action was taken.

Powell worked with the French, giving ground by agreeing the council would meet to discuss any defiance by Hussein. But Powell insisted that any nation could determine that Baghdad was in violation - and then attack Iraq.

One compromise came Nov. 3, when Dominique de Villepin, the French foreign minister, spoke with Powell by phone. Even with possible war hanging in the balance, the secretary was the average nervous father, preparing to escort his daughter at her wedding. With the deal with France sealed, Powell tucked the phone away and strode down the aisle.

Showing that diplomacy can hang on a single word, French and Russian opposition persisted as late as Thursday. Fewer than 24 hours before the vote, Powell and his team agreed to change a word - from or to and. The and/or issue set the final push in motion.

Powell spoke again with de Villepin. Bush called President Jacques Chirac of France.

With the French on board by Thursday afternoon, Powell called Foreign Minister Igor Ivanov of Russia, who, said one U.S. official, considered the switch from and to or to be "a breakthrough" that he would immediately take to President Vladimir V. Putin.

Ivanov told Powell he would get back to him.

Nor did Powell receive definitive word from Syrian officials, who were urging a delay in the vote and did not say how they would vote if the council proceeded.

The vote was not yet unanimous. Two nations were holding out.

Early yesterday, Powell received a call from Ivanov.

Was Russia on board?

"Khorosho - da." Ivanov told Powell. That is Russian for "Very good - yes."

Syria came on board just minutes before the vote.

"And that was 15-0," a relieved administration official said. "We had gotten a pretty good outcome on this vote."