DENVER — Senator McCain kept his vice presidential pick a closely guarded secret hours before the high-stakes announcement today as top prospects seemed to drop away and speculation moved to darkhorse candidate Alaska Governor Sarah Palin.

Two GOP strategists close to the McCain campaign said all indications pointed to Palin, a self-styled “hockey mom” and political reformer. The strategists spoke on condition of anonymity because they were not authorized by the McCain camp to discuss the matter. There was no confirmation from McCain or his advisers.

With an announcement scheduled in Dayton, Ohio, an associate of Minnesota Governor Tim Pawlenty said the governor had been informed he is not Mr. McCain’s pick. The official spoke on condition of anonymity because he was not authorized to speak for Mr. Pawlenty, who had all but ruled himself out.

“I’m not going to be there. I plan to be at the state fair. You can draw your conclusion from that,” Mr. Pawlenty said on his weekly call-in radio show on WCCO-AM in Minneapolis. He also called it “a fair assumption” that he will not be Mr. McCain’s running mate.

Associates close to former Massachusetts Governor Mitt Romney were saying the same thing, telling The Associated Press that the former presidential candidate had not been offered the job by McCain.

Ms. Palin is a first-term governor credited with reforms of her out-of-the-way state. Newly minted Democratic nominee Senator Obama is making an aggressive play for the traditional GOP stronghold and its three electoral votes, and polls show the race close.

At 44, Mr. Palin is younger than Mr. Obama and, like Mr. McCain, she calls herself a maverick.

A Gulfstream IV from Anchorage, Alaska, flew into Middletown Regional Airport in Butler County near Cincinnati about 10:15 p.m. last night, said airport manager, Rich Bevis. He said several people came off the plane, including a woman and two teens, but there was no confirmation of who was aboard.

“They were pretty much hustled off. They came right down the ramp, jumped in some vans here and off they went,” Mr. Bevis said. “It was all hush, hush.”

Among the other possible running mates: former Pennsylvania Governor Tom Ridge, Democrat-turned-independent Senator Joe Lieberman of Connecticut and former Representative Rob Portman of Ohio.

The Arizona senator decided on his choice for vice president early yesterday, but the campaign has given no hint on the selection that will be announced on his 72nd birthday. The speculation sent a buzz throughout Denver, where Mr. Obama accepted his party’s nomination and put Senator Joe Biden of Delaware on his ticket.

McCain’s communications director, Jill Hazelbaker, gave nothing away during an interview on CBS’ “The Early Show.”

“John McCain is going to make the choice from his heart. He’s going to choose someone who can be a partner in governing. He’s going to choose someone who brings character and principle to the table and who shares his priorities. And I’m confident that he’s going to make a great pick,” Ms. Hazelbaker said.

Republicans kick off their national nominating convention next week in St. Paul, Minn., and Mr. McCain’s campaign hopes the announcement of his running mate will stunt any momentum Mr. Obama might get from the just-concluded Democratic National Convention.

Mr. McCain was mum on the subject yesterday as he and his wife, Cindy, boarded a plane in Phoenix bound for Dayton.

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Associated Press writers Glen Johnson in Boston and Doug Glass in Minneapolis contributed to this report.