NEW YORK -- Republican presidential nominee-to-be John McCain on Tuesday sparred with David Letterman during a taping of his "Late Show."

Letterman joked during his monologue that the senator from Arizona reminded him of "the guy at the hardware store who makes the keys" and of "the guy who can't stop talking about how well his tomatoes are doing."

After he added that McCain looked like "the guy who points out the spots they missed at the car wash," the senator appeared on stage.

"You think that stuff's pretty funny, don't you?" McCain asked.

He tossed at Letterman: "Well, you look like a guy whose laptop would be seized by the authorities."

McCain also said the host resembled the guy caught smuggling reptiles in his pants, to which Letterman replied, "Don't knock it if you haven't tried it."

The White House hopeful also compared Letterman to the manager of a creepy motel, the guy who enjoys watching his swim trunks inflate in a hot tub and the guy about whom neighbors later say, "He mostly kept to himself."

Later in the show, the two discussed more serious issues, including the national credit crisis, Iraqi casualties, the U.S. prison for terrorist suspects at Guantanamo Bay, Cuba, the government's bailout of investment firm Bear Stearns and accusations that McCain is not a true conservative Republican.

"I think maybe some people think that you ought to have exactly the same position they have on every issue," McCain said.

Among Democratic presidential candidates, Sen. Hillary Rodham Clinton of New York appeared on "Late Show with David Letterman" in February, and Sen. Barack Obama of Illinois was a guest in January.