DENVER -- Republican presidential nominee-in-waiting John McCain stayed mum about his pick of a running mate Thursday and one top prospect, Minnesota Gov. Tim Pawlenty, abruptly canceled numerous public appearances.

Others believed to be in contention for the No. 2 slot on the GOP ticket included former Massachusetts Gov. Mitt Romney, who was meeting with donors throughout California, and Democrat-turned-independent Sen. Joe Lieberman of Connecticut, who was vacationing on New York's Long Island.

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.

McCain, however, was uncharacteristically silent.

As McCain and his wife, Cindy, boarded a plane in Phoenix bound for Dayton, Ohio, reporters shouted a barrage of questions at the senator about whether he'd made up his mind.

McCain wasn't biting. He flashed a double thumbs-up and boarded the plane.

The GOP nominee-in-waiting is widely expected to name his running mate in the coming days, perhaps as early as Thursday night or Friday. He and his No. 2 are expected to appear together for the first time at one or more rallies planned for Ohio, Pennsylvania and Missouri in the run-up to Monday's convention kickoff.

In an interview aired Thursday morning, McCain said he still hadn't made up his mind. Far from quieting speculation, this only fueled it as he sought to siphon attention from Democrat Barack Obama's acceptance of the presidential nomination in Denver by playing coy.

He told KDKA NewsRadio in Pittsburgh in an interview taped Wednesday: "I haven't decided yet so I can't tell you."

McCain, who spoke with the radio station from his home in Arizona, told people late Wednesday that he wasn't going to make a final decision until after he talked with his wife. She has been in the country of Georgia this week and returned late Wednesday.

With both the eventual pick and the effort to keep buzz alive beforehand, McCain's campaign hopes curb any uptick in polling that Obama might get from his convention and to create momentum heading into the gathering of GOP delegates for McCain next week in St. Paul, Minn.

Pawlenty, in Denver to criticize Democrats on McCain's behalf, canceled without explanation an afternoon roundtable interview with the AP as well as other media interviews. Questioned about the vice presidential selection earlier, Pawlenty would only say that he is to be in Minnesota on Friday for the state fair. He had cautioned during a series of morning TV interviews that while speculation might be fun, "most of it turns out to be inaccurate."

Romney, who had played the GOP attack-dog role earlier in the week at the Democratic convention and has been meeting with donors in California, left his beachfront San Diego home Thursday morning with an overnight bag. His son, Matt, said Romney was headed to an unspecified location in the state. Asked about being vice president, the elder Romney said: "I don't have anything for you right now."

Ridge was at his suburban Washington, D.C., home. Asked by an AP photographer as he took out the trash if he had any travel plans for the day, Ridge smiled and said he didn't.

One Lieberman aide said there has been no indication he is the choice. For instance, no staff have been called to join him at his vacation site.

For months, McCain's vice presidential search process has been kept closely held by a small group of his advisers. But details have been trickling out this week.

This includes word from two Republicans that McCain met with his senior advisers in Arizona on Wednesday to discuss the pick, conflicting information about whether or not he had settled on a choice, and the campaign's announcement it would air a TV ad in battleground states around when Obama will be giving his prime-time acceptance speech. A spokeswoman said McCain would be shown speaking directly to the camera with a message aimed at Obama but would not disclose the content.

Inside GOP circles Thursday, though, speculation swirled around Lieberman. It was fueled by reports that McCain's advisers had asked for additional detailed information from Lieberman, by McCain's close friendship with the 2000 Democratic vice presidential nominee, and by word that Republican operatives had been told to prepare for the possibility of an "unconventional" choice.

GOP strategist Karl Rove late last week encouraged Lieberman to withdraw his name from vice presidential consideration, but Lieberman rejected the suggestion, according to a person familiar with the phone call, who requested anonymity because he was not authorized to speak publicly about it. Rove, through a spokeswoman, denied he made the call.

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Associated Press writers Glen Johnson in Boston, Mike Glover in Phoenix, and Andrew Miga and photographer Scott Applewhite in Washington contributed to this story.