A Republican presidential debate scheduled for live national television coverage will be missing two of the GOP's leading contenders for the nomination.

Former New York Mayor Rudy Giuliani and former Massachusetts Gov. Mitt Romney both say they have more important campaign commitments scheduled.

"We have six events on that date that are already scheduled," Giuliani told a Miami radio talk show host on Friday, adding that CNN arbitrarily picked the Sept. 17 date without checking with the candidates.

As part of an arrangement with the video-sharing Web site YouTube, questions for the debate would come from the online video community, an element Romney seems uneasy about.

"I think the presidency ought to be held at a higher level than having to answer questions from a snowman," Romney said earlier this week, referencing a Democratic event held in South Carolina on Monday that included a question about global warming from a snowman.

Romney, however, blamed a scheduling conflict for skipping the Florida event slated for the newly renovated Mahaffey Theater along the city's downtown waterfront.

Gov. Charlie Crist said he hopes to persuade Romney and Giuliani to change their minds so they can attend the debate in the state holding the fourth largest number of electoral votes.

Arizona U.S. Sen. John McCain, former Wisconsin Gov. Tommy Thompson and Texas Rep. Ron Paul have agreed to participate in the St. Petersburg event.

The state GOP also is planning a primary debate in Orlando in October, to be broadcast on Fox.

Florida's presidential preference primary election is scheduled for Jan. 29.