WASHINGTON — Republican presidential candidate Fred Thompson has been crisscrossing the country since early this summer on a private jet lent to him by a businessman and close adviser who has a criminal record for drug dealing.

Thompson selected the businessman, Philip Martin, to raise seed money for his White House bid. Martin is one of four campaign co-chairmen and the head of a group called the "first day founders."

Thompson's frequent flights aboard Martin's twin-engine Cessna 560 Citation have saved him more than $100,000, because until the law changed in September, presidential candidates could reimburse private-jet owners for just a fraction of the true cost.

Martin entered a plea of guilty to the sale of 11 pounds of marijuana in 1979; the court withheld judgment pending completion of his probation. He was charged in 1983 with violating his probation and with multiple counts of felony bookmaking, cocaine trafficking and conspiracy. He pleaded no contest to the cocaine-trafficking and conspiracy charges, which stemmed from a plan to sell $30,000 worth of the drug, and was continued on probation.

Thompson said Sunday that he was unaware of Martin's criminal past but that he wouldn't "throw my friend under the bus" for decades-old indiscretions.

Thompson said he learned about Martin's past on Saturday, and understood that the crimes were committed when Martin was in his 20s and living in Florida, before moving to Tennessee, where the two became friends.

"I know Phil is a good man. He is my friend. He is going to remain my friend," Thompson said when questioned on NBC's "Meet the Press."

"He didn't go to jail, he got probation, he's paid his debt to society and turned himself around and become a good, productive, successful citizen."

Martin, 49, could not be reached for comment Sunday.

He is one of several top political fundraisers with a criminal past to gain access this year to a presidential contender. Sen. Hillary Rodham Clinton decided in September to return more than $800,000 raised by Norman Hsu, one of her top bundlers, after newspapers disclosed that he had been convicted of fraud and had an outstanding warrant for his arrest.

Martin has been more than just a key fundraiser to Thompson, though. The use of his plane eases a major logistical burden stemming from the intense demands on presidential candidates this year for appearances in more than 20 states holding early primaries. It also may have saved the campaign at least $120,000, given that Federal Election Commission rules allowed Thompson to reimburse Martin for the use of the private jet at the commercial ticket rate until Congress changed the rules in September.

Thompson has reported reimbursing Martin $102,330, without specifying precisely where he flew on the plane, or when. But a comparison of flight records for the plane, kept by the tracking firm FlightAware, and news accounts of Thompson's campaign appearances this year, show that since June the plane has made more than two dozen stops that coincided with Thompson campaign events.

The Web site JetTrip.com estimates that the hourly charter rate for use of a plane similar to Martin's would be between $1,500 and $2,400, which means these flights normally would cost at least $220,000, more than double what Thompson paid.

Information from The Associated Press in included in this report.