BY GAIL EPSTEIN NIEVES

TAMPA - Democrat Betty Castor this morning conceded defeat to Republican Mel Martinez in the down-to-the-wire race to capture the U.S. Senate seat vacated by fellow Democrat Bob Graham.

Castor said she called Martinez about 10:30 a.m. to concede.

''I have wished him well,'' she said at an 11 a.m. news conference here. "I have congratulated him and told him if there is any way I can be helpful to him in the weeks and months ahead, I would like to do that.

''We both talked about how divided this state is and how divided the nation is,'' she said. "I assured him that I did not want to get into any kind of a prolonged debate over who wins this state.''

Martinez edged out the former legislator and university president by more than 76,000 votes out of more than 7.1 million cast statewide. His margin of victory was by more than 1 percent of the vote -- just outside the threshold requiring a recount.

Castor said she would monitor the counting of absentee ballots statewide, but doesn't expect the result to change.

''Even if every vote is counted, we think it would be very difficult to make up the difference,'' she said.

Martinez, 58, who left President Bush's Cabinet as housing secretary to run for the Graham's seat, becomes the nation's first Cuban-American senator.

Martinez -- who has scheduled a 2 p.m. press conference in Orlando -- needed the strong support of Hispanic voters to win the seat. Also affecting the outcome of the race was stealth candidate Dennis Bradley of the Veterans Party, who garnered about 2.3 percent of the vote.

The White House helped, too, loaning him advice and advisors from the earliest days of the campaign.

The Martinez victory leaves the Democratic Party holding on one statewide position -- the other U.S. Senate seat held by Bill Nelson, who did not face re-election this year.

Castor said this is likely her last run for statewide office, including the governor's job.

''I don't believe my name will be on another ballot,'' she said. "I think that others can energize the party ... and be successful.''

Had she won, Castor would have been the first Democratic woman to represent Florida in the U.S. Senate and only the second female senator in the state's history.