Influential Republican Senator John McCain announced Wednesday that he will run for the White House in the 2008 race. McCain, who lost his party’s nomination in 2000 to now-President George W. Bush, made the announcement on an unusual venue: CBS television’s “Late Show with David Letterman,” a popular comedy show.

“I am announcing that I will be a candidate for president of the United States,” McCain said on the show.

He later said that he will be making the formal announcement in April. “You drag this out as long as you can,” he said, half-joking. “You don’t just have one rendition.”

The outspoken Arizona senator, 70, once a front-runner among Republican faithful, has seen his standing in the polls slip. A Wednesday survey placed him well behind his main rival, former New York mayor Rudolph Giuliani.

McCain has long supported the unpopular

Iraq war, arguing that more soldiers were needed to flush out insurgents, crush militias and train Iraqi forces — a position since taken up by the president.

A former Navy pilot and Vietnam prisoner of war, McCain even called for more US troops in Iraq following the November 2006 elections that saw Republicans lose control of both chambers of Congress on voter unhappiness with the war.

A poll Wednesday however showed the senator lagging behind Giuliani, known as “America’s Mayor” for his handling of the September 11, 2001, terror attacks on New York.

Giuliani scored 44 percent support, against 34 percent on January 19, according to the ABC News/Washington Post poll. McCain slipped six points, from 27 percent in January to 21 percent.

The senator described Giuliani on CBS as a “genuine American hero” and “a very formidable candidate.”

Any chances of being another candidate’s running mate? “I spent all those years in a North Vietnamese prison camp, kept in the dark, fed scraps — why the heck would I want to do that all over again?” he told Letterman.

In mid-February McCain traveled to conservative South Carolina and delivered a hawkish speech supporting US efforts in Iraq. “I can’t guarantee success, but I can guarantee the consequences of failure,” McCain said. “If we leave Iraq, you would see chaos; you would see genocide. And sooner or later we would be back.”

At the event he took a broadside at one of the main architects of the Iraq war. Former secretary of defense Donald Rumsfeld “will go down in history as one of the worst secretaries of defense in history” for his “mismanagement” of the war, McCain said.

Vice President

Dick Cheney defended his longtime friend Rumsfeld two days later. “John’s entitled to his opinion. I just think he’s wrong,” Cheney said in an interview with ABC News. “I think he (Rumsfeld) did a superb job in terms of managing the

Pentagon under extraordinarily difficult circumstances.”

McCain, who pulled an upset victory in a Republican nominating event early in the 2000 presidential race, was savaged by supporters of then-Texas governor Bush when he reached South Carolina.

Anonymous e-mail messages and fliers began to circulate questioning McCain’s conservatism, his patriotism and his personal life, even accused him of fathering illegitimate children and his wife of being a drug addict.

McCain counter-attacked, accusing two powerful evangelical Christian leaders, Jerry Falwell and Pat Robertson, of being “agents of intolerance” and “corrupting influences” in American politics. A day later, he attacked “the evil influence that they exercise over the Republican Party.”

McCain lost the South Carolina primary, and eventually lost the nomination to Bush.

Despite their differences, McCain strongly supported Bush’s 2004 presidential re-election — ignoring hints that Democrat

John Kerry, another Vietnam war veteran, wanted him as a running mate — and has since been mending fences with his party’s conservative base.

In May 2006 McCain even spoke to students graduating from evangelical leader Falwell’s Liberty University in Lynchburg, Virginia.

Differences with Falwell, Robertson and their supporters, he said at the time, “should remain an argument among friends . . . I have not always heeded this injunction myself, and I regret it very much.”