Alaska Gov. Sarah Palin announced yesterday that she would quit her job at the end of the month, unleashing a torrent of speculation about her plans, motivation, and the political wisdom of such a seemingly confounding decision.

Speaking from the backyard of her lakefront home in Wasilla, Alaska, Palin suggested she would remain active in national politics. "We know we can effect positive change outside of government," she said in making the announcement, flanked by her husband, Todd, and members of their family.

Many observers took that to mean a full-fledged run for the Republican presidential nomination in 2012, without the encumbrance of her office and the difficulty of navigating a national campaign from thousands of miles away.

But the fact that Palin, 45, will vacate the Alaska governor's office without finishing her first four-year term or bolstering her thin political resume - which was a detriment during her 2008 vice presidential bid - led some analysts to suggest the move would badly damage any future political aspirations.

"I always thought after the race what she needed to do was go back to Alaska and be substantive, show she's got a grasp of government and work for the good of the folks back home," said Stuart Rothenberg, an independent campaign analyst in Washington. "This seems to be the exact opposite."

Palin experienced a meteoric rise after Sen. John McCain of Arizona plucked her from relative obscurity to serve as his running mate. She was a smash hit at last summer's Republican National Convention. But her image suffered after a series of unsteady campaign appearances.

She remains a favorite of social conservatives, who traditionally have exerted strong influence over the GOP nomination. But Palin draws a visceral contempt from many Democrats, political independents, and even some Republicans - among them some McCain advisers who bared their sentiments, anonymously, in a recent unflattering article in Vanity Fair magazine.

Palin seemed to allude to those attacks at her impromptu news conference yesterday. "You are naive if you don't see a full-court press from the national level picking away a good point guard," said Palin, who was famously aggressive in her days as a high school basketball star.

She spoke in that cryptic fashion throughout her appearance, saying her decision to step down had been some time in the making, although she never clearly spelled out why. "Many just accept that lame-duck status, and they hit that road. They draw a paycheck. They kind of milk it. And I'm not going to put Alaskans through that," Palin said.

She said that her successor, Lt. Gov. Sean Parnell, would be sworn in at the governor's picnic in Fairbanks this month. He was among the people stunned by her move; Parnell said he learned of Palin's decision only Wednesday evening.

"It's a gob-smacking, jaw-hit-the-ground, total kind of surprise," said Ivan Moore, an independent political pollster in Anchorage who said Palin was a strong favorite to win a second term as governor had she run next year.

As for any presidential ambitions, "I can't see how this move helps her," Moore said. "In fact, quite the opposite. I think it's terribly damaging."

Not everyone agreed.

Republican strategist Scott Reed, unaffiliated for 2012, said that yesterday's announcement could be a good thing because it allows Palin to turn the page and start rebuilding her image.

He described the Vanity Fair piece as a "hit job" that showed her she had to shake things up. Stepping down "allows her to begin to draw a new narrative on herself," he said.

"If anything," this "allows her to have a brand new day, a fresh start, and she can shake all these cobwebs from the last campaign and her term as governor and start over," he said.

Jerry McBeath, a veteran political science professor at the University of Alaska Fairbanks, called the pending resignation a "smart move" for Palin and the state.

"Alaska is an isolated stage from which to operate if you want to figure in American national politics. I don't know what she has in mind. Some TV show or some national radio show. There are opportunities for her, I'm sure."

But political analyst Larry Sabato, in Charlottesville, Va., said that Palin's announcement left many confused.

"It's absolutely bizarre, and I think it eliminates her from serious consideration for the presidency in 2012," he said.

Palin said her family weighed heavily in her decision.

"I polled the most important people in my life, my kids, where the count was unanimous," she said. "Well, in response to asking, 'Hey, you want me to make a positive difference and fight for all our children's future from outside the governor's office?' It was four yesses and one 'Hell, yeah!' And the 'Hell, yeah' sealed it."