She made the announcement standing with her family. At one point she described how her children had voted in favor of her doing this — "Four yeses and one 'Hell, yeah!' " she said — suggesting that the family had had enough of the scrutiny that has made them tabloid staples.

But at another point she invoked a military leader in what seemed to be an effort to wave aside any suggestion that she was abandoning the fight. "Take the words of Gen. MacArthur," she said. "He said, 'We're not retreating. We are advancing in another direction.' " The quotation actually is attributed to another Korean War commander, Maj. Gen. Oliver P. Smith of the U.S. Marines.

Later in the afternoon, as questions reverberated around Republican circles about what exactly she intended to do, she posted a notice on her Twitter site, reading: "We'll soon attach info on decision to not seek re-election … This is in Alaska's best interest, my family's happy … It is good, stay tuned."

The statement she eventually posted recounted what she called her accomplishments as governor.

Palin is one of a number of Republican governors who are possible contenders for the party's presidential nomination in 2012 whose terms expire in 2010.

Many Republican strategists have argued that it would be difficult for someone to run for governor in 2010 and turn around immediately, while running a state, and run for president in 2012. Gov. Tim Pawlenty of Minnesota announced last month that he would not seek re-election when his term expires in 2010, as he considers a race for president.

Quitting midterm, however, is highly unusual. It set off a round of speculation about what led her to leave office so abruptly. One interpretation among Republicans was that she had simply underscored how erratic she is as a politician.

"Good point guards don't quit and walk off the floor if the going gets tough," said John Weaver, a former senior strategist for McCain. "Today's move falls further into the weirdness category; people don't like a quitter."

But some of her supporters argued that this could actually provide Palin an opportunity to recover from what has been a damaging year for her, and prepare herself for the 2012 race. She has been enmeshed in continuing battles with members of both parties in her Legislature.

The sheer distance of Alaska from the rest of the country complicated her ability to take care of the most basic kind of presidential preparation work: going to Republican Party state dinners, developing a network of fundraisers and supporters, and becoming educated about the issues she might face as a presidential candidate.

In addition, Palin just signed a lucrative contract to write a book.

"I think she is trying to determine how she can better get to where she'd like to be," said Speaker Mike Chenault of the Alaska Legislature, a Republican from the Kenai Peninsula. "And she figures that if she resigns, people can't be taking so many potshots at her."