John McCain has selected his running mate and will hold a rally with that person Friday at noon in Dayton, Ohio, FOX News confirms.

The identity of McCain's vice presidential selection is still unknown, but the presumptive GOP presidential nominee made the decision Thursday and is expected to shortly notify his selection, according to campaign manager Rick Davis.

McCain is now en route from Phoenix to Dayton, as rival Barack Obama is set to accept the Democratic presidential nomination in Denver. It is unclear whether the campaign will make known his selection before or during the rally.

A McCain aide, speaking on condition of anonymity, said earlier that McCain may announce his choice on Thursday.

Obama spokesman Dan Pfeiffer told Politico.com that it would be "political malpractice" for McCain to leak his running mate on the same night as Obama's historic speech.

"It won’t make much of a difference to struggling American families who John McCain chooses to be the next Dick Cheney if he continues to insist on being the next George Bush," Obama spokesman Hari Sevugan said in a statement.

The list of candidates has narrowed considerably. Topping that list are former Massachusetts Gov. Mitt Romney and Minnesota Gov. Tim Pawlenty.

Pawlenty stirred widespread speculation by clearing his schedule of interviews and other appearances Thursday. FOX News has confirmed he still intends to do his weekly radio show from Minneapolis Friday.

But Pawlenty batted back the vice presidential talk.

"I have refrained from answering questions relating to the vice presidential selection process. We're going to allow Senator McCain to make that announcement and the McCain campaign to unveil it at their own time and under their own circumstances," he said Thursday.

Romney was meanwhile meeting with donors throughout California, and Democrat-turned-independent Sen. Joe Lieberman of Connecticut, another possible pick, was vacationing on Long Island.

Romney's family was reportedly being given Secret Service security sweeps, but the Secret Service denied that claim late Thursday afternoon.

Former Pennsylvania Gov. Tom Ridge, too, was still a possibility, as was the idea that McCain would choose a dark horse from any number of names that have circulated.

U.S. Sen. Kay Bailey Hutchison, though, said Thursday she hasn't been asked to be McCain's running mate, despite some speculation that she's a possible choice for the No. 2 spot on the Republican ticket. And former Secretary of State Colin Powell was apparently never vetted for the job.

McCain said in an early morning radio interview Thursday that he was bringing both Ridge and Romney to a rally on Saturday in Pennsylvania. At the time he told KDKA NewsRadio in Pittsburgh he hadn't yet decided on his running mate. But he cautioned against assuming that meant either one would be the pick.

Asked to hint which way he is leaning, McCain turned -- as he has for days -- to a joke, saying it would be actor Wilford Brimley.

"He's a former Marine and great guy and he's older than I am, so that might work," said the four-term Arizona senator who turns 72 on Friday.

McCain also talked glowingly of Ridge, a longtime friend who has been a frequent presence at his side during the campaign.

"He's a great American and a great and dear friend and I rely on him and I have for many years," McCain said.

Insiders say McCain still is considering Lieberman, who ran as Al Gore's vice presidential running mate in 2000, but now backs McCain.

It could be a long shot. A Lieberman spokesman coyly declined to comment Wednesday on the senator's vice presidential prospects -- or his whereabouts.

"He's on vacation. I've been told that's all I'm allowed to say. He's on vacation," a spokesperson for the senator told FOX News.

"I'll even go one step further with you than I've gone with other reporters," the source continued. "He's on planet Earth."

FOX News' Carl Cameron and Trish Turner and The Associated Press contributed to this report.