A somber George W. Bush assured the nation last night that he had won the U.S. presidential election, mere hours after the state of Florida finally certified his victory.

But Vice President Al Gore '69 will formally contest the Florida certification today and a profusion of local and federal court challenges are pending, 20 days after voters cast their ballots.

Addressing a nationwide television audience from Texas last night, Bush pointedly urged Gore to withdraw his legal protests and concede the election. He also named his vice presidential candidate, Dick Cheney to head his transition team and announced that former Mass. state representative Andrew Card would be his chief of staff.

"Now that the votes are counted, it is time for the votes to count," Bush said.

"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," he said.

Just after 7 p.m., Florida Secretary of State Katherine Harris declared Bush to be the state's official winner, by a margin of 537 votes, of the state's presidential contest last night.

Moments later Democratic vice presidential candidate Joseph I. Lieberman said that Gore's campaign would formally challenge the results of the Florida election.

Lieberman said that Harris had held "an incomplete and inaccurate count," giving the vice president no choice but to contest the certification.

"How can we teach our children that every vote counts if we are not willing to make a good-faith effort to count every vote?" Lieberman said.

Former Secretary of State James Baker, who is spearheading the Bush effort, promptly fired back, emphasizing that the Texas Governor had been declared the winner of Florida at each step of the drawn-out legal battle.

"At some point there must be closure," Baker said. "At some point the law must prevail, and the lawyers must go home. We have reached that point."

At the long-awaited certification announcement, state officials tried, without a hint of facetiousness in their voices, to emphasize that Florida's tumultuous election had finally come to an end.

"Yogi Berra said it's not over 'til it's over. Well, it's over," said Florida's Secretary of Agriculture Bob Crawford.

And with the Florida win, Bush technically has won 271 electoral votes and the nationwide election--but a continuing set of legal battles ensures that the presidency will not be definitely decided for at least one more week.

"We're now in a two-week-or-so period in which you have a contest on both sides of this election," said Rep. Richard A. Gephardt, the House minority leader.

Besides continuing court challenges in Florida from both sides, the U.S. Supreme Court on Friday will hear Bush's case against a Florida state Supreme Court decision that allowed hand recounts to continue.

Lieberman did not specify the reasons for Gore's contest of the election, but lead Gore lawyer David Boies said it would be based on at least three grounds, all involving incomplete recounting or votes he said had been tallied for the vice president at some point and later discounted.

The Gore campaign will challenge the Palm Beach board's recounting method in court today, complaining they used too stringent a standard to determine which votes were valid.

Boies told press assembled in Tallahassee that Gore will also contest

certification because of the decision last Wednesday by Miami-Dade County canvassers to drop their recount and because ballots that had been judged to be for the vice president there and in Nassau County were subsequently subtracted from his total.

Gore is expected to outline his reasons for his contest of the election in a speech today.

Yesterday, with time running out before the 5 p.m. deadline for submitting final vote tallies to Harris' office, Palm Beach remained 800 to 1,000 ballots short of finishing its hand recount. The Palm Beach canvassing board then requested that Harris include its partial recount in her final tally, but Harris denied the request. The partial recount would have given Gore a net gain of 180 votes.

Board members had met in round-the-clock sessions the since early Saturday morning in hopes of completing a re-canvass of 14,500 questionable ballots, but simply ran out of time.

Harvard Democrats said they saw no reason for Gore to concede the election, even as pressure for them to do so mounts from some Democrats.

"In reality, the certification doesn't mean that Bush wins Florida's

election votes," said Harvard College Democrats President Marc Stad '01, who added that Florida law gives Gore time to contest.

Stad said the Florida Supreme Court ruled that they wanted the intent of the voter to be determined, but did not give enough time for recounts to be carried out.

"What we need is a complete and accurate hand recount. That's the most

accurate way to determine how many people voted for each candidate," he said. "Once [Miami-Dade is] counted, it will put Gore over the top."

--Material from the Associated Press was used in the reporting of this article.