Paring down the list could take weeks, possibly months, McCain, R-Ariz., says.

"It's not an unusual thing," he said while campaigning in Maryland. "You put the list together, and then you just could do a cursory kind of a look that I guess you could do on Google."

McCain said he would like to name a running mate by the GOP convention, CNN reported.

McCain also discounted statements by a Christian conservative leader that he hasn't united Republicans.

James Dobson, Focus on the Family founder, said in a statement he didn't think McCain "is successfully unifying the Republican Party or drawing conservatives into his fold."

McCain told CNN he disagreed, citing endorsements by former rivals and polling data indicating the party is rallying behind him.

"I'm very pleased at the polling data that shows that our party is very unified," McCain said. "More Republicans say they'll vote for me than Democrats say that they will vote" for Sens. Barack Obama, D-Ill., or Hillary Clinton, D-N.Y., who are battling to become the party's nominee.