DAYTON, Ohio – Aiming to at once appeal to conservatives and women, Republican presidential candidate John McCain on Friday named Alaska Gov. Sarah Palin his running mate – a move as unprecedented as it was unexpected.

"To be chosen brings a great challenge. I know it'll demand the best I have to give, and I promise nothing less,” Ms. Palin said to a jubilant, if bewildered Wright State University Nutter Center crowd of about 15,000.

Mr. McCain described her as a fellow “maverick” who “understands the problems, the hopes of working people.”

His selection of a woman vice presidential candidate means that for the first time in U.S. history, only two of the four major party candidates in this year's presidential race are white men – Mr. McCain himself and Democratic vice presidential nominee Joe Biden. Democratic presidential nominee Barack Obama is multiracial.

Ms. Palin, 44, is likewise the first woman to appear on a Republican presidential ticket, and only the second woman after Democrat Geraldine Ferraro, Walter Mondale's running mate in 1984, to appear on a major party slate.

AP File

Alaska Gov. Sarah Palin offers the GOP ticket youth and robust conservative credentials – something it until now arguably lacked.

View larger Photography Photo store

She offers the GOP ticket youth, glamour and robust conservative credentials – something it until now arguably lacked.

In acknowledging the significance of her selection, Ms. Palin first noted Ms. Ferraro's distinction. She also praised U.S. Sen. Hillary Clinton for "such determination and grace" during her failed Democratic presidential nomination bid this year.

"Hillary left 18 million cracks in the highest, hardest glass ceiling in America," Ms. Palin said playing on Ms. Clinton’s oft-used line about the number of Democratic primary votes she received.

But with her own candidacy, Ms. Palin vowed, "We can shatter that glass ceiling."

Ms. Clinton, for her part, released a statement Friday afternoon saying Americans should “be proud of Gov. Sarah Palin's historic nomination, and I congratulate her and Senator McCain. While their policies would take America in the wrong direction, Gov. Palin will add an important new voice to the debate.”

Ms. Palin’s ascension to national prominence is little short of stunning. Until now, most Americans outside Alaska had never seen her face, or heard her name, even as her home state approval rating routinely exceeds 80 percent.

As a candidate her own party establishment didn’t initially support, Ms. Palin won Alaska's governorship in 2006 on a platform of reform, having unsuccessfully bid for lieutenant governor in 2002.

She served stints as a city council member in and mayor of tiny Wasilla, Alaska, and as head of the Alaska Oil and Gas Conservation Commission, before leading one of the nation’s least populous states – about twice as many people live in Dallas than Alaska.

It’s a public service acumen that’s hardly extensive – even a liability, perhaps, for Mr. McCain, who for months has derided Mr. Obama as a political lightweight lacking the requisite experience to lead the nation.

Personally, Ms. Palin is a former basketball star known as “Sarah Barracuda” for her tenacious on-court style. She entered beauty pageants and earned a communications/journalism degree from the University of Idaho. She’s an avid hunter and outdoorswoman, and her oldest son, Track, serves in the U.S. Army.

Politically, she opposes abortion and gay marriage, supports gun rights and boasts a history of fighting corruption within her own party.

Many Democrats are nonplussed with Ms. Palin.

“McCain is pandering to the right-wing evangelical part of the Republican Party, and he’s pandering to women who supported Hillary Clinton and he thinks are stupid enough to vote for his ticket even though he’s anti-women issues,” said Dallas County Democratic Party Chairwoman Darlene Ewing, herself a Clinton delegate to the Democratic National Convention. “And this puts to rest the Obama experience argument. You could put her resume on a three-by-five index card.”

House Speaker Nancy Pelosi, the highest-ranking elected woman in the nation, said Mr. McCain’s selection “raises serious questions about his judgment. “Why, when the country is fighting two wars, facing an uncertain economy and an energy crisis, did Senator McCain make the choice that he did?” Ms. Pelosi wrote. “Sarah Palin is not the right choice. She shares John McCain’s commitment to overturning Roe v. Wade and continuing George Bush’s failed economic policies.”

Indeed, until Friday morning, conservative Minnesota Gov. Tim Pawlenty appeared primed to receive Mr. McCain's nod, with former Massachusetts Gov. Mitt Romney also in contention. Former Pennsylvania Gov. Tom Ridge and U.S. Sen. Joe Lieberman, an independent from Connecticut, also remained rumored.

All are political veterans.

But Mr. McCain insisted that Ms. Palin is exactly the kind of running mate he sought.

"I've spent the last few months looking for a running mate who can help me shake up Washington," Mr. McCain said. "I had many good people to choose from, all of them dedicated to this country to getting us back on the road to prosperity and peace … and I have found the right partner."

Ceding that Ms. Palin isn’t yet a national figure, Mr. McCain said, “when you get to know her, you're going to be as impressed as I am. She knows where she comes from, and she knows who she works for … She's exactly who I need. She's exactly who this country needs."

Campaign staff said Mr. McCain offered Ms. Palin a spot on the ticket at 11 a.m. Thursday at his home in Sedona, Ariz. He first met Ms. Palin in February at a National Governors Association meeting, and last Sunday, the two spoke over the phone, the campaign said.

Mr. McCain, wife Cindy at his side, began is public introduction of Ms. Palin at 11:17 a.m. Friday as Van Halen's "Right Now" reverberated through the Dayton arena.

The crowd attempted to sing him "Happy Birthday" as he began his speech – Mr. McCain is turning 72 – but he quickly hushed them.

A heckler then tried shout Mr. McCain down as he introduced Ms. Palin, still off-stage, her husband and four of five children with her. Mr. McCain ignored the man and kept speaking. Security quickly removed the man.

President Bush said in a statement that “Governor Palin’s success is due to her dedication to principle and her roll-up-your-sleeves work ethic and serves as a wonderful example of the spirit of America. By selecting a working mother with a track record of getting things done, Senator McCain has once again demonstrated his commitment to reforming Washington.”

U.S. Sen. John Cornyn, R-Texas, described Ms. Palin as “true agent of change who brings a breath of fresh air to Washington from far outside-the-beltway.” Texas Gov. Rick Perry said that “compared to Joe Biden’s life-long opposition to energy exploration, her energy experience is proof that she is the right choice for this country.”

And Dallas Log Cabin Republican President Rob Schlein hailed the selection as a harbinger of changes within the Republican Party.

"She can help McCain win, and will appeal to independent and younger voters," said Mr. Schlein, whose organization represents gay Republicans. "She is a mainstream Republican who will unite the party and is an inclusive Republican that will help the ticket's appeal to conservative gay and lesbian voters."