ST. PAUL, Minn. – In picking little-known Sarah Palin as his running mate, Republican John McCain is betting, among other things, that having a woman on his ticket will make some voters take a new look at the race.

The possible upsides are clear-cut, and so is the potential risk that her inexperience undercuts McCain's charge that Democratic presidential nominee Barack Obama is not ready to be president.

"She's the ultimate high-risk, high-reward choice," said Peter Brown, the assistant director of the Polling Institute at Connecticut's Quinnipiac University. "She's a game changer either way."

Palin, 44, former mayor of Wasilla, Alaska, and first-term governor of Alaska, is a new face on the national scene, and she might catch on with the voters. Her credentials as a social conservative will help reassure and perhaps energize a Republican base that has reservations about McCain.

Palin has a reputation as a reformer and someone who is not beholden to her party. Her selection bolsters McCain's maverick image.

California Gov. Arnold Schwarzenegger says he likes Palin, calling her a reformer with the strength to "push back." He commended her stance against Alaska's congressional delegation on earmarks for the "Bridge to Nowhere," which became a national symbol of wasteful, pork-barrel spending.

Palin's personal narrative as a working mother raising five children, including an infant with Down syndrome, with a husband who belongs to a union, might prove attractive to working-class voters in battleground states who have been suspicious of Obama.

And her presence on the ticket will allow Republicans to argue that Obama would not be the only one to break barriers if elected.

"He's chosen a Washington outsider who will be an ally for him in shaking up the way things are done," said Ron Nehring, chairman of the California Republican Party.

The obvious intent of her selection, confirmed by her own words Friday, is to appeal to one of the larger groups of undecided voters in the race – women upset that Hillary Rodham Clinton is not on the Democratic ticket.

But it seems unlikely that women who backed Clinton would be drawn to the other party by a woman who is a strong opponent of abortion rights and any number of other Clinton positions.

Clinton herself stayed relatively quiet Friday, issuing a crisp statement heralding Palin's position on the GOP ticket. "We should all be proud of Governor Sarah Palin's historic nomination, and I congratulate her and Senator McCain," she said. "While their policies would take America in the wrong direction, Governor Palin will add an important new voice to the debate."

The selection of Palin, with 20 months experience leading a state with 670,000 residents, undercuts one of the most effective arguments the McCain campaign has against the Democrats, that Obama is not ready to be president.

The unavoidable question now is whether Palin is ready – and why McCain would want a running mate of whom that question could legitimately be asked. McCain turned 72 on Friday and has a history of skin cancer.

"On his 72nd birthday, is this really the one-heartbeat-away he wants to put in the White House?" said Rep. Rahm Emanuel of Illinois, the No. 3 Democratic in the House. "What does this say about his judgment."

On Thursday in Denver, with Barack Obama in mind, Minnesota's Republican Gov. Tim Pawlenty said: "When you look at a candidate, you should ask two questions: What have you done, and what have you run? And when you look at those two questions, the answers are 'not much' and 'nothing' "

In Palin's case, Democrats were saying Friday, the answers might well be 'not much' and 'very little.'

In an intriguing coincidence, Palin and her Democratic counterpart, Joe Biden, have sons in the military heading to Iraq this fall, a shared experience that might flavor their Oct. 2 vice presidential debate in St. Louis in different ways when it comes to national security.

Analysts also were already wondering how Palin, who made a point of mentioning Friday that she is the commander of the Alaska National Guard as governor, will do in that debate against Biden's 36 years in the Senate. She might benefit from low expectations.

Some Republicans maintained that Palin would get the better of Biden, predicting that the veteran senator, who is known for his slashing attacks, would have a hard time not looking as though he was being condescending to a woman.

"In a way, McCain has set a trap on the experience argument," said Scott Reed, who managed Bob Dole's presidential campaign in 1996, "because if they start picking on her on experience, it's going to backfire with women."

The naming of Palin also should also end, once and for all, the idea that it matters where a running mate comes from.

After eight years of a vice president from Wyoming, the nation is now looking at a successor from either Delaware or Alaska. Each has three electoral votes, the minimum under the Constitution.

The New York Times, McClatchy Newspapers and Washington Post contributed to this report.