John McCain made it clear Wednesday he has little interest in holding any more debates with GOP rival Mike Huckabee before the March 4 primaries, which could push him over the numerical threshold needed for the Republican presidential nomination.

Huckabee, who is trailing McCain by more than 700 delegates, challenged the Arizona senator to debate in a letter Tuesday.

"We have a pretty hard and fast schedule," McCain said Wednesday. "We've debated 16 times so we'll examine it ... but frankly I doubt it."

Huckabee asked McCain to join him for a "Lincoln-Douglas-style debate so that voters can better understand our views on critical issues such as health care, education, energy independence, terrorism and national security."

He noted that Obama and Hillary Clinton have had that opportunity -- the two Democrats debated in Cleveland Tuesday night for their 20th and last time before March 4.

"It seems only fitting to me that Republican primary voters are offered the same," Huckabee wrote.

McCain had said earlier in the day that his campaign never heard from Huckabee about a debate, despite the fact that Huckabee has been making the request publicly since Mitt Romney dropped out.

McCain is instead focusing on Democratic presidential front-runner Barack Obama, who traded jabs with him Wednesday over comments Obama made at Tuesday's debate about fighting Al Qaeda in Iraq. McCain has sharpened his focus on Obama as he's racked up victories over Huckabee, and has challenged the Illinois senator on his support of earmarks and his hedging on a pledge to use public financing in a general election.

Despite their good relations, Huckabee has said repeatedly he will challenge McCain until the GOP convention in Minnesota in September. A week ago, Huckabee defended McCain during the uproar over a New York Times article that linked him to a female Washington lobbyist.

Polls show Huckabee has not faded away in Ohio and Texas, which vote March 4.

An American Research Group poll from Feb. 23-24 showed McCain with a slim 4-point edge over Huckabee in Texas, leading 45 to 41 percent. The same group showed McCain with an 11-point lead in Ohio.

Senior staffers told FOX News that while the American Research Group polls can differ wildly at times, the crowds for Huckabee have been considerably bigger than the crowds for McCain; a sign, they say, that Huckabee is gaining formidable ground in the Lone Star state.

FOX News' Serafin Gomez and Mosheh Oinounou contributed to this report.