Harris is expected to be a heavy favorite in the state's Republican-dominated 13th Congressional District.
"In light of the recent tragedy, I am more committed than ever to serving this president and our nation," Harris said. "As a nation we have united to overcome this challenge and the bonds of our courage and strength to do what is right inspires us to succeed."
The seat came open with the retirement of Rep. Dan Miller, R-Fla. The district is comprised mainly of Republicans and independents that traditionally vote with the GOP.
"Given her role in the recount, she is extremely popular in that district," said Tramm Hudson, chairman of the Sarasota Republican Party. "I doubt there will be any credible opposition."
The only other candidate in the district so far is 27-year-old Republican Chester Flake, a computer consultant.
Harris, 44, became a nationwide Republican favorite in the aftermath of the 2000 general election, which hung on Florida's electoral votes.
She declared President Bush the winner, although the campaign of former Democratic Vice President Al Gore was insisting on a recount of the votes.
The Florida Supreme Court overruled her, but the U.S. Supreme Court stepped in and declared Bush the winner. The Republicans won the election in Florida by a 537-vote margin.
Harris had been rumored as a candidate for a diplomatic post in the Bush administration, but that never materialized. That was considered as a political risk in some Republican circles.
But she has remained visible, attending high-profile Washington social functions and accepting frequent offers to speak around the country.
Democrats in Florida who already have written off the district said they welcomed the announcement. They have used her for months as their favorite verbal target.
"She's one of the best get-out-the-vote weapons we have," cracked Tony Welch, a spokesman for the state Democratic Party.
Harris won the election for Secretary of State in 1998 in a bitter primary battle with Republican opponent Sandra Mortham. But that same year, Floridians voted to eliminate the office after her first term and fold it into the governor's office.
Harris has faced controversy recently, firing her inspector general and taking criticism for being a free spender. According to media accounts, her staff members frequently traveled overseas in first class airline seats rather than coach, violating state guidelines.
She also was accused of using her office equipment to campaign for Republicans last fall and in the election aftermath, but a subsequent investigation by a group of media outlets found little evidence of any significant abuse
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