Florida Republicans Gov. Charlie Crist and State House Speaker Marco Rubio are locked in a heated primary for Sen. Mel Martinez‘s U.S. Senate seat, and “Fox News Sunday” might soon have Chris Wallace moderate a debate between the two.

According to the Chicago Tribune’s The Swamp, Rubio has already agreed and a date has been set — March 28th on “Fox News Sunday” — but Gov. Crist has yet to accept.

It would be a big get for “Fox News Sunday,” which is coming off its best performance ever in the D.C. market thanks to a big snowstorm and a big sit-down Wallace conducted with Sarah Palin in Nashville.

We noted yesterday that NBC’s David Gregory and CBS’ Bob Schieffer weighed in on the Sunday show race, with Schieffer saying it had become “a three-way dogfight.” While FOX broadcast numbers are still lower for “FNS” than programs on the big three, Wallace’s show is now besting CBS in some top 25 markets year-to-date including Dallas, Atlanta, Detroit, and Tampa. “FNS” also gets a boost from replays on Fox News Channel.

We’ll have the final numbers for Sunday’s shows this Thursday.