(Reuters) - A planned March 1 debate of Republican presidential candidates in Atlanta was canceled Thursday after Mitt Romney and Ron Paul dropped out of it and the campaign for Rick Santorum expressed doubt he would attend.

The CNN-sponsored debate was scheduled to take place in Newt Gingrich's home state of Georgia. Of the four remaining candidates for the Republican presidential nomination, only Gingrich, who has generally done well in the debates, had definitely been scheduled to attend.

A CNN statement said Romney and Paul had sent word they would not participate, and without full participation of all four candidates, CNN will not move forward with the Super Tuesday debate.

The Republican state-by-state campaign to seek a challenger to President Barack Obama has been heavily reliant on debates. There have already been 20 debates, with one more scheduled for next Tuesday in Mesa, Ariz. It too is sponsored by CNN.

Romney spokeswoman Andrea Saul said Romney would be spending a lot of time campaigning in Georgia and Ohio before the March 6 Super Tuesday contests when 10 states vote.

With eight other states voting on March 6th, we will be campaigning in other parts of the country and unable to schedule the CNN Georgia debate. We have participated in 20 debates, including eight from CNN, she said.

(Reporting By Steve Holland; Editing by Peter Cooney)

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