Updated

The top four Republican presidential candidates have set off a debate over whether the GOP is paying enough attention to blacks and Hispanics by skipping Thursday night's debate on minority issues.

The four leading Republican candidates -- former New York Mayor Rudy Giuliani, Fred Thompson, Arizona Sen. John McCain and Mitt Romney -- cited scheduling conflicts in saying they could not attend the debate at Morgan State University, a historically black college.

The forum, moderated by talk show host Tavis Smiley and featuring black and Hispanic journalists as panelists, was to air live on PBS.

The candidates expected to attend are all long shots for the nomination: Sen. Sam Brownback of Kansas, Mike Huckabee, Reps. Duncan Hunter of California, Ron Paul of Texas and Tom Tancredo of Colorado. Conservative activist Alan L. Keyes, who announced his candidacy last week, also said he would attend.

Among the Republicans who have criticized the candidates for skipping the forum are former House Speaker Newt Gingrich, R-Ga., and former Maryland Lt. Gov. Michael Steele, the first black official elected statewide.

"I'm puzzled by their decision. I can't speak for them. I think it's a mistake. I wish they would change their minds -- they still have a few days -- and I wish they would in fact go to the debate Thursday night," Gingrich, who is considering entering the race for the GOP nomination, said earlier this week.

Smiley moderated a debate in June among the Democratic presidential candidates at Howard University in Washington, D.C., another historically black school.

Earlier this month, seven of eight Democratic candidates participated in a debate aired by Univision, the Spanish language TV network. A Univision-sponsored GOP debate was canceled after only McCain agreed to participate.