Florida Rep. Katherine Harris (R) announced Tuesday that she will challenge Sen. Bill Nelson (D) in 2006, setting up a blockbuster contest that will draw national money and attention.

In a statement, Harris said she is “humbled by the task ahead” and promised to “tell it like it is, and do what’s right.”

She plans to formally launch her campaign next month.

“Today, after months of encouragement from friends and constituents, colleagues and advisors, many prayers, and with the love and support of my family, the time has come to launch a campaign for the United States Senate,” Harris said. “I am confident that I can accomplish more for the people of Florida, and experience reminds me I’ve always done best when I started out as the underdog.”

Harris — who has been vilified by Democrats for the role she played in the 2000 presidential election as Florida secretary of state — might describe herself the underdog, but is certain to attract unparalleled national media attention. Her presence transforms Nelson’s first re-election race into a national contest — and potentially a referendum for both parties.

Nelson’s allies wasted little time framing the matchup as one of moderation versus extremism.

“In over three decades of public service, Bill Nelson has always strived to help everyday people and has represented mainstream Florida values,” said Nelson spokesman Dan McLaughlin. “Katherine Harris represents only the radical right.”

Dave Beattie, Nelson’s pollster, said Harris’ entry into the race would not affect the freshman Senator’s overall strategy.

“I don’t think it kind of changes anything that Nelson’s planned on for winning, which is talking about what he’s done and how he’s represented the state,” he said. “I think that she clearly is a known figure and has clearly wanted to do this for a couple of years.”

Harris has been mulling a run for Senate for almost two years and deferred an open-seat bid in 2004 at the urging of White House officials.

While polling done earlier this year has shown that Harris would be hard to beat in a Republican primary, those same surveys have indicated that the sophomore lawmaker would not be the party’s strongest nominee against Nelson.

A Republican poll done in mid-April showed Nelson leading Harris 48 percent to 41 percent. By comparison, the same poll found Nelson in a virtual dead heat in hypothetical matchups with either state Attorney General Charlie Christ or Chief Financial Officer Tom Gallagher. Both Christ and Gallagher are running for governor in 2006 and are unlikely to change course, especially given Harris’ entrance in the Senate race.

Some Republicans had privately hoped that Harris would be deterred from running in 2006 and that Gallagher, Crist or Lt. Gov. Toni Jennings could be persuaded to run for Senate.

A statement released by the National Republican Senatorial Committee on Tuesday made no mention of Harris by name, and held the door open to the possibility that other Republican candidates could still emerge.

“Sen. Nelson is very vulnerable and this race will continue to attract the attention of a lot of candidates for that reason,” NRSC spokesman Brian Nick said. “The NRSC is committed to winning this seat and will put in the necessary resources to do so.”

Resources are not likely to be a problem for either Harris or Nelson next year. Third party interest groups are also expected to play an active role on both sides in the contest.

In two years in the House, Harris has become a fundraising star because of her ability to tap into a national donor network.

She raised and spent more than $3 million on her past two Congressional campaigns and had $253,000 in the bank as of March 31.

Nelson, meanwhile, already has $3 million stockpiled for the race.

Florida is a large state with several expensive media markets, making it highly plausible that each candidate could end up spending in the range of $20 million on the race.

While Republican strategists fear that Harris may turn off some of the state’s more moderate voters, there is no doubt she would solidify the Republican base and make it harder for Nelson to pick off some votes.

“She remains a polarizing figure statewide, and the Republicans that would be open to a state Democrat are probably going to be pretty solidly on her side just because of [their] allegiance to [President] Bush,” said one Democratic operative. “They would overcome that allegiance for probably someone else but she’s so identified [with Bush] that nothing has to be done to strengthen that connection.”

Most Democrats, however, are relishing the thought of a race against Harris, even though it could draw needed resources away from contests in other states.

“We look forward to hearing Rep. Harris explain why she has been such a polarizing figure,” said Democratic Senatorial Campaign Committee spokesman Phil Singer.

But while the DSCC openly mocked Harris for her past — “Why does controversy follow Katherine Harris wherever she goes?” blared its Tuesday news release — party leaders instead chose to play up Nelson.

DSCC Chairman Charles Schumer (N.Y.) specifically avoided taking on Harris for her past controversies, suggesting that Nelson had a tough race ahead of him regardless of his opponent.

“We know it’s going to be a tough fight, but we think Bill is going to prevail,” Schumer said. “We think Bill is in good shape.”

Senate Minority Leader Harry Reid (D-Nev.) brushed aside Harris and other GOP opponents, simply declaring, “Nelson’s gonna win.”

Freshman Sen. Mel Martinez (R-Fla.), who emerged from a bruising primary last year against former Rep. Bill McCollum and others, said he is hoping that the eventual nominee will not have to go through the “gauntlet” he had to run in 2004, a draining experience both financially and politically.

“I would hope that we could avoid a divisive primary,” said Martinez, whose campaign was sharply criticized for late ads that attacked McCollum’s conservative credentials on social issues such as gay marriage.

Martinez, who was notified by Harris on Tuesday morning about her intentions, said he is all but certain to stay out of a competitive primary if more Republicans emerge.

“I came out of a campaign recently, and I’m not anxious to get back into one,” he said. “I don’t anticipate being involved.”

Meanwhile, jockeying in the race to succeed Harris in the Sarasota-based 13th district is already under way.

On the Republican side, former Sarasota County Republican Party Chairman Tramm Hudson is all but certain to jump in the House race. Auto dealer Vern Buchanan has also said he would consider running for Harris’ seat if she vacated it.

Hudson, who recently ended a six-year stint as county GOP chairman, is a close ally of former Rep. Dan Miller (R), who held the seat from 1992 through 2002.

Hudson is close friends with former Rep. Bill Paxon (R-N.Y.) and his wife, former Rep. Susan Molinari (R-N.Y.). Paxon said Tuesday that he is already helping to plan a Washington, D.C., fundraiser for his friend’s campaign.

“We’re going to be very active,” Paxon said. “I just got off the phone with him and he’s going to run. I would suspect unless something surprising happens he’ll be the 800-pound gorilla in this race.”

Buchanan is the president and CEO of Sarasota-based Buchanan Automotive Group and a major GOP donor. He served as Martinez’s finance chairman during his 2004 Senate campaign.

Both Hudson and Buchanan considered running for the 13th district seat when Miller retired in 2002 but deferred to Harris.

Among Democrats, former banking executive Christine Jennings, who was favored by national party leaders to take on Harris in 2004, is running again. Jennings failed to get past attorney and 2002 nominee Jan Schneider in the Democratic primary last year. Schneider may also run again.

Paul Kane contributed to this report.