DAYTON, Ohio -- Sen. John McCain has chosen Alaska Gov. Sarah Palin to be his running mate -- the first female candidate for vice president in the history of the Republican Party.

Palin was considered a long shot for the ticket, but her selection is being applauded by social conservatives whose support McCain needs to win the White House.

McCain introduced his running mate before an enthusiastic crowd in swing state Ohio.

"She's got the grit, integrity, good sense and fierce devotion to the common good that is exactly what we need in Washington today," McCain said.

Palin is a conservative, anti-abortion Christian and self-described "hockey mother" of five.

"This is a moment when principles and political independence matter more than just the party line," Palin said.

In a message perhaps aimed at undecided female voters, Palin praised Sen. Hillary Clinton's historic bid for the Democratic nomination.

"It turns out the women of America aren't finished yet, and we can shatter that glass ceiling once and for all," Palin said.

The choice of Palin stunned even the shrewdest political observers.

"There's a fundamental problem here,” said political analyst Marc Sandalow. “She undermines the central tenant of the McCain attack on the Democrats, which is that Barack Obama does not have the experience to lead."

Critics pointed to Palin's lack of experience on the national stage and in foreign policy.

"While we obviously have differences over how best to lead this country forward,” said Democratic presidential nominee Barack Obama, in a statement, “Governor Palin is an admirable person and will add a compelling new voice to this campaign."

Other leading Democrats seized on the experience issue. Sen. Chuck Schumer called Palin a “roll of the dice” and said the thought of her assuming the presidency is troubling.

Alaska lawmakers are investigating whether Palin abused her power in the firing of a public safety commissioner. They're looking into whether it was payback because the commissioner refused to fire a state trooper who was going through a messy divorce with Palin's sister.

Palin has something in common with the Democratic vice presidential nominee Sen. Joe Biden. Both are parents of soldiers who are deploying to Iraq in the next two months.

Palin will formally accept the nomination during the Republican National Convention, which is scheduled to kick off on Monday in St. Paul.