Sen. Mel Martinez, R-Fla., who had previously said he would not seek reelection in 2010, announced on Friday that he will resign his seat as soon as a replacement is selected, probably by the end of the month. Martinez, a former chairman of the Republican National Committee and a secretary of housing and urban development under President George W. Bush, said at a news conference in Orlando that he wants to spend more time with his family. 'There's no impending reason; it's only my desire to move on,' Martinez said. He said the decision, which surprised Senate colleagues, came 'of my own free will.' Under Florida law, Gov. Charlie Crist, R, will appoint a replacement to serve the remainder of Martinez's term. Crist is running for the seat in next year's election and is leading in polls. He is expected to tap a caretaker who will hold the seat until January 2011 but not seek a full term. Crist is all but certain to name a Republican to replace Martinez. That would leave intact the current Senate balance of 40 Republicans and 60 senators who generally vote with Democrats. Martinez, 62, cited family considerations and a desire to leave politics when he announced last year that he would not run in 2010. He did not say Friday why he decided to step down now. He said he does not have a new job lined up, and he hinted that he will remain in political life, saying, 'I look forward to being an active part of a resurging Republican Party.' Florida Republicans say potential candidates to serve out the remainder of his term include former Gov. Bob Martinez and former state Secretary of State Jim Smith, both Republicans. For the 2010 election, Rep. Kendrick Meek is the leading Democratic candidate. Crist is being challenged among Republicans by former Florida House speaker Marco Rubio, who could make an issue of whomever Crist taps as a replacement for Martinez. 'As Governor Crist considers who he will appoint as Florida's next U.S. senator, I urge him to take great care in his selection,' Rubio said in a statement. Martinez follows Alaska Gov. Sarah Palin, R, and Sen. Kay Bailey Hutchison, R-Texas, in taking the unusual step of leaving office without completing a full term. Hutchinson has said she will resign this fall to focus on challenging Texas's Republican governor next year; Palin has not made clear whether she plans to seek political office. 