Texas Gov. George W. Bush claimed victory last night in the presidential race, after he was certified the winner of Florida's election by 537 votes out of nearly 6 million cast.

Vice President Al Gore refused to concede and announced that he would try to reverse the outcome in court.

"I will work to unite our great land," said Bush, in a five-minute television address from the state Capitol in Austin, Texas. "This has been a hard-fought election, a healthy contest for American democracy. But now that the votes are counted, it is time for the votes to count."

He "respectfully" called on Gore to reconsider his plan to contest the election. A further legal challenge "is not the best route for America," Bush said.

Bush moved to make himself the de facto president-elect by requesting that President Clinton allow him to open a transition office in Washington.

"Time runs short and we have a lot of work to do," Bush said.

He said his transition team would be headed by his running mate, former Defense Secretary Dick Cheney, and that former Transportation Secretary Andrew Card would be his chief of staff.

Bush's request could force Clinton into the awkward position of taking sides in the continuing election fight. Up to now, neither Bush nor Gore has been given the keys to various transition offices around the nation's capital, and the Clinton administration has held off any liaison activities with either candidate.

"The election was close. But tonight after a count, a recount and yet another manual recount, Secretary Cheney and I are honored and humbled to have won the state of Florida, which gives us the needed electoral votes to win the election," said Bush, whose margin over Gore in Florida amounted to less than one one-hundredth of a percentage point.

"We will therefore undertake the responsibility of preparing to serve as America's next president and vice president," added Bush, who did not, however, refer to himself as president-elect.

The 54-year-old Republican spoke in broad terms about his desire to see the nation's political leaders "come together to do the people's business." He repeated several of his major campaign themes and repeated his intention to reach out to Democrats.

With Congress more evenly divided between the two parties than at any time in nearly a half-century, bipartisanship will be a governing necessity for the new president. But with Democrats already lining up behind Gore's effort to win the Florida vote in the courts, it will be some time before the two sides can come together.

Gore plans to address the nation today from Washington, to explain his decision to challenge the official count and plead for time. Sen. Joseph I. Lieberman, the Democratic vice presidential candidate, said in nationally televised remarks that Gore and he had "no choice but to contest" the election.

Lieberman described the certified result as, "by any reasonable standard ... an incomplete and inaccurate count."

The Democrats' hopes for winning the election now seem to depend on persuading Florida's courts to order a new count of presidential ballots in Miami-Dade County, which aborted its hand recount last week after officials there concluded that they could not meet yesterday's 5 p.m. deadline.

Winning Florida's 25 electoral votes would give Bush a total of 271 electoral votes. That is one more than the majority needed to claim the presidency and the second- smallest victory margin since the advent of the two-party system in the mid-1800s.

Bush would also become only the third man to win the White House after losing the popular vote. Gore currently leads by more than 337,000 votes nationwide, according to the latest unofficial total by the Associated Press.

When Florida Secretary of State Katherine Harris pronounced Bush the winner in a nationally televised signing ceremony, a cheer went up from Bush supporters outside the Florida state Capitol.

The certified result, which Harris indicated that she considers less proper than the 930-vote margin she would have certified earlier, included newly revised counts from 11 counties. Bush gained at least 65 votes from largely Republican counties, while Gore picked up 567 from a final hand count in heavily Democratic Broward County.