33"She's exactly who I need. She's exactly who this country needs to help me fight the same old Washington politics of 'Me first and country second,' " McCain declared as the pair stood together for the first time at a boisterous rally in Ohio just days before the opening of the party's national convention.

"Politics isn't just a game of competing interests and clashing parties," added Palin, 44, who has built her career in large measure by challenging fellow Republicans.

In the increasingly intensive presidential campaign, McCain made his selection six days after his Democratic rival, Barack Obama, named Sen. Joseph Biden of Delaware, as his No. 2 on the ticket.

The contrast between the two announcements was remarkable -- Obama, 47, picked a 65-year-old running mate with long experience in government and a man whom he said was qualified to be president. The timing of McCain's selection appeared designed to limit any political gain Obama derives from his own convention, which ended Thursday night with his nomination acceptance speech before an estimated 84,000 in Invesco Field in Colorado.

Public opinion polls show a close race between Obama and McCain, and with scarcely two months remaining until the election, neither contender can allow the other to jump out to a big post-convention lead.

On his 72nd birthday, McCain chose Palin, a woman younger than two of the Arizonan's seven children and a person who until recently was the mayor of small-town Wasilla, Alaska, and has been governor less than two years. He settled on her six months after first meeting the governor and following only one phone call between them last Sunday and a single face-to-face meeting Thursday, according to a timeline provided by his campaign.

The Obama campaign immediately questioned whether she would be prepared to step in and be president if necessary.

"Today, John McCain put the former mayor of a town of 9,000 with zero foreign policy experience a heartbeat away from the presidency," Adrianne Marsh, a spokeswoman for Obama, said in a written statement. A statement was put out on Obama's plane with the candidate merely welcoming her to the campaign.

President Bush complimented McCain for "an exciting decision."

"Governor Palin is a proven reformer who is a wise steward of taxpayer dollars and champion for accountability in government," a presidential statement said. "By selecting a working mother with a track record of getting things done, Senator McCain has once again demonstrated his commitment to reforming Washington."

Sen. Hillary Rodham Clinton, who came so close to being the first major party woman presidential candidate, said in a statement: "We should all be proud of Gov. Sarah Palin's historic nomination, and I congratulate her and Sen. McCain. While their policies would take America in the wrong direction, Gov. Palin will add an important new voice to the debate."

"It's an absolutely brilliant choice," said Mathew Staver, dean of Liberty University School of Law. "This will absolutely energize McCain's campaign and energize conservatives," he predicted.

Palin's name had not been on the short list of people heavily reported upon by the news media in recent days, and McCain's decision was a well-kept secret until just a couple hours before Friday's rally.

McCain's campaign said that Palin and a top aide met with senior McCain advisers in Flagstaff, Ariz., on Wednesday night. The next morning, the campaign said McCain formally invited Palin to join the ticket on the deck of McCain's home near Sedona, Ariz., and later Thursday the governor flew to Middletown, Ohio, with staff to await Friday's event in Dayton.

Describing the process that led to her selection, Palin told reporters she'd received word that she was McCain's choice on Thursday and had met privately with him that day to discuss it. She spoke briefly as the two running mates surprised shoppers at the Buckeye Corner in Columbus, Ohio, where they purchased Ohio State University sports memorabilia. McCain and Palin started a bus tour across Ohio and to Pittsburgh, where they will hold a campaign rally Saturday. Ohio and Pennsylvania are two states that figure prominently in who wins the election this fall.

Asked why McCain chose her, his campaign manager Rick Davis said, "Part of it is personal fit."

"He sees Sarah, Governor Palin, as the future of the party," he added. "These are people he'd like to elevate in that regard -- reformers."

Sharyl Odenweller, a retired teacher from Delphos, Ohio, who was visiting the store, said she was pleased that McCain had chosen a woman and someone "very pro life." But, Odenweller also said, "I'd like to know more about her experience. If something happened to him, would she be qualified to step into the presidency?"

With his pick, McCain passed over more prominent contenders like former Massachusetts Gov. Mitt Romney and Minnesota Gov. Tim Pawlenty, as well as others such as former Pennsylvania Gov. Tom Ridge, whose support for abortion rights might have sparked unrest at the convention that opens Monday in St. Paul, Minn.

A self-styled hockey mom and political reformer, Palin became governor after ousting a state chief executive of her own party in a primary.

More recently, she has come under the scrutiny of an investigation by the Republican-controlled legislature into the possibility that she ordered the dismissal of Alaska's public safety commissioner because he would not fire her former brother-in-law as a state trooper.

Palin has a long history of run-ins with the Alaska GOP hierarchy, giving her genuine maverick status and reformer credentials that could complement McCain's image.

Her husband, Todd Palin, is part Yup'ik Eskimo, and is a blue-collar North Slope oil worker who competes in the Iron Dog, a 1,900-mile snowmobile race. The couple lives in Wasilla. They have five children, the youngest of whom was born in April with Down syndrome.

• Associated Press Writer Liz Sidoti reported for this story from Denver.