HOUSTON -- Trying to give his troubled candidacy a fresh start, President Bush defiantly predicted last night that he is on his way to the biggest political upset since Harry S. Truman won re-election more than 40 years ago.
Mr. Bush broke with tradition by making a lengthy speech to Republican delegates on the first day of the party's convention here. The move was aimed at firing up supporters deeply dispirited by polls that show Democratic nominee Bill Clinton leading the president by a wide margin.
"I don't care what the polls say," Mr. Bush told the crowd in a hall adjacent to the Astrodome, the convention site. "I am a fighter, and I intend to fight for what's right for America."
The four-day convention opened yesterday morning with routine approval of a party platform that included a strong anti-abortion provision. Abortion-rights Republicans lacked the numbers needed to challenge the plank on the floor, and it was approved without debate.
Last night's session was highlighted by a strongly worded endorsement of Mr. Bush by conservative Patrick J. Buchanan, his rival in the primaries, and a nostalgic bow by former President Ronald Reagan.
In a harsh assault, Mr. Buchanan described last month's Democratic convention in New York as "20,000 liberals and radicals . . . dressed up as moderates and centrists" in "the greatest single exhibition of cross-dressing in American political history."
Mr. Buchanan's 30-minute speech, delivered with considerable relish, contained a sneering, sardonic critique of the Democratic ticket. Mr. Clinton, he said, was a a draft dodger who lacked "the moral authority to send young Americans into battle."
He also assailed Mr. Clinton's wife, Hillary, saying that she and her husband are on the wrong side of a religious and cultural war for the soul of America.
He claimed the Clintons would impose an agenda of "abortion on demand, a litmus test for the Supreme Court, homosexual rights, discrimination against religious schools, women in combat."
But Mr. Buchanan also had some gentle criticism of Mr. Bush's leadership during the longest recession since the 1930s.
Describing working-class Americans as "conservatives of the heart," the television commentator advised Republicans: "We need to reconnect with them. We need to let them know we know how bad they're hurting. They don't expect miracles of us, but they need to know we care."
Mr. Buchanan, whose endorsement of Mr. Bush drew a standing ovation from, among others, Barbara Bush, was frequently interrupted by cheers and chants such as "Go Pat, go Pat."
Mr. Reagan, in a more traditional GOP critique of liberal Democrats, said the country "cannot afford to take a chance" on Mr. Clinton.
Mr. Reagan echoed Mr. Buchanan's description of the Democratic nominee as "slick."
Deriding what he termed the "rhetorical smoke" emanating from the Democratic side, Mr. Reagan advised voters to "follow the example of their nominee -- Don't inhale," a reference to Mr. Clinton's description of his youthful experience with marijuana.
The oldest man ever to serve as president poked fun at himself as well as at Mr. Clinton as he dismissed Democratic comparisons of the Arkansas governor to Thomas Jefferson, the nation's third president.
"Well, let me tell you something. I knew Thomas Jefferson. He was a friend of mine. And governor, you're no Thomas Jefferson," he said, playing on Sen. Lloyd Bentsen's retort to Dan Quayle in the 1988 vice-presidential debate. The crowd in the Astrodome roared with delight, as a grinning Mr. Quayle rose to his feet, applauding.
In an address laced with many famous lines from his old convention speeches dating back to 1964, Mr. Reagan endorsed his former vice president "warmly, genuinely, wholeheartedly."
"We need George Bush," said the former president, who delivered his lines crisply, if slightly hoarsely.
"Goodbye," he said, with his wife, Nancy, at his side, at the conclusion of his 36-minute appearance on the podium, as red, white and blue balloons floated down from the rafters.
The stage was set for last night's Clinton-bashing by Mr. Bush's free-swinging speech to his supporters shortly after his arrival in Houston, his adopted home town.
Before a crowd of several thousand supporters in the AstroArena, Mr. Bush cast himself as a candidate who always runs best when he is behind and forecast an upset win in November that would be "the most stirring political comeback since Harry Truman gave 'em hell in 1948."
Mr. Bush promised to copy Truman's strategy of attacking Congress as he travels the country this fall, a shift that apparently reflects the influence of James A. Baker III, the president's new campaign manager. In recent months, as Bush campaign themes seemed to change daily, he had backed away from the idea of blaming Congress for the nation's problems.