Secretary of State Colin L. Powell has been a soldier and a four-star general, a national security adviser and a man who could have won a presidential nomination if he had desired it. Yet little in his four decades of pubic service places him as much in the spotlight as when he steps before the U.N. Security Council Wednesday to make the Bush administration's case against Iraq.

Powell staked his reputation within the administration on the need to win U.N. approval for military action against the government of President Saddam Hussein. Now he must sway not only the votes of the 15 diplomats seated at the horseshoe table in the Security Council chamber, but also win over public opinion around the globe to the view that Iraq has violated its international obligations to disarm and that war is justified.

Powell's public position on military action has appeared to turn much more hawkish in recent weeks, confounding Europeans and other skeptics of war. Many had viewed Powell as a moderating influence in an administration stocked with hardliners on Iraq. People close to Powell say the shift in tone stems from frustration with some U.S. allies, particularly France, the need to emphasize that diplomatic options have about run their course and the realization that President Bush is mentally ready to go to war.

Powell, a soldier at heart, believes strongly in the concept of duty. The president backed him on going to the United Nations, Powell has told associates, and he will back the president on war if it comes to that.

Powell's two years as secretary of state have at times been deeply frustrating to him. He is respected by the career staff at State for winning more funding and prestige for the department, but he has had to slog through his share of policy battles with the White House, Defense Department and Vice President Cheney's office. Often, he may lose an initial policy fight, only to see things turn his direction months later.

"We win more than we lose, but it just takes so damn long to get there," one senior State Department official said.

To this day, Powell has no regrets about not seeking the presidency and has closed off that possibility in his mind, friends said.

Yet Powell is a confident man and he believes that he might yet win a second U.N. Security Council resolution authorizing military force against Iraq, officials said. He is banking on his speaking skills, the credibility he has built over the years and the weight of the evidence he will present. The evidence, administration officials said, will include photographs, intercepted communications and other documentation of Iraqi concealment of banned chemical, biological and nuclear weapons programs as well as Iraqi government ties to terrorism. Bush has said he is ready to go to war with or without another U.N. vote.

In drafting his speech, officials said, Powell was aware that he must address not only the foreign ministers and U.N. ambassadors in the Security Council chamber but also skeptics in the media and in Congress who have demanded evidence of Iraqi transgressions. In addition, Powell wants to send an unambiguous message to Iraq.

Powell also wants to avoid devaluing his credibility. A Gallup poll released this week found, for instance, that 63 percent of Americans said they were more likely to trust Powell than the president on Iraq policy, compared with 24 percent who said they would more likely trust Bush. Powell, who lists as one of his rules, "check small things," has repeatedly pressed intelligence analysts on the quality of their information, interpretations and translations.

"He doesn't want to put information in there that he's not comfortable with," a senior official said. Powell also purposely drew on information that other permanent members of the Security Council -- Britain, France, Russia and China -- have received through their own intelligence services, the official added.

Richard L. Armitage, deputy secretary of state, said last week the evidence in the speech would reflect an old Navy saying: "KISS: 'Keep it simple, sailor,' go with your strong points."

Powell devoted nearly eight weeks last fall to winning a unanimous resolution giving Iraq a last chance to disarm. At this point, he has little sympathy for the Security Council members who threatened Hussein with "serious consequences" in the November resolution and now are reluctant to approve the use of force to topple him. He is especially angry at the French foreign minister, Dominique de Villepin, who took Powell by surprise two weeks ago when he publicly appeared to close off the option of imminent war during a U.N. conference that Powell attended. Powell thought it was a serious tactical misjudgment that let Hussein believe the United Nations was too divided to confront him.

Powell privately told diplomats from Security Council countries last fall that their endorsement of Resolution 1441 meant the United States would expect them to authorize the use of force if Iraq defied them. "You can't be afraid to go down this road because the going's going to get tough or hard," Powell said he told the Security Council. "You should have realized that was a possibility when you signed on and you became a party to 1441."

F. William Smullen, a long-time Powell aide who served as his chief of staff at the State Department until last summer, said Powell almost certainly crafted a phrase or statement that will capture his essential point. "In this age, we live from one sound bite to the next," he said. "You want something that's memorable and dominates the broadcasts."

During the Persian Gulf War in 1991, when Powell was chairman of the Joint Chiefs of Staff, he gave a war briefing that is still remembered for its evocative expression of how the U.S. military planned to deal with the Iraqi army: "First, we're going to cut it off, and then we're going to kill it."

Smullen said Powell sat at his desk the afternoon of that briefing, scribbling on a notepad, as he worked and reworked the phrase, considering and rejecting such words as neutralize, attack and destroy before he settled on kill. In his memoirs, Powell noted with satisfaction that he gave a deliberately understated briefing but his "punch line" dominated the news the next day.

Powell's performance will also be judged against history -- the moment on Oct. 25, 1962 when Adlai Stevenson, the U.S. ambassador to the United Nations, pulled out photographs showing to the Security Council that the Soviet Union had deployed nuclear missiles in Cuba. Powell has said he "would love to have that kind of material to present."

"We talk about it a lot," Powell told reporters last week. "But whether there will be a 'Stevenson photo' or 'Stevenson presentation' that would be as persuasive as Adlai Stevenson was in 1962, that I can't answer."

Retired Marine Gen. Anthony C. Zinni, who is close to Powell, said people should not underestimate Powell's competitive instincts. Zinni thought Powell's authoritative voice could provide the tipping point for a number of nations looking for a reason to back the United States on Iraq.

"He likes to win," said Zinni, who served as an envoy for Powell last year. "That was one of the things he told me when he sent me out to the Middle East: 'We like to win,' with a little smile on his face."

Slevin reported from Washington. Staff writer Bob Woodward in Washington contributed to this report.

Secretary of State Colin L. Powell, left, meets with diplomats at the United Nations a day before his Security Council address.