WASILLA, Alaska — Even for a nonconformist, Alaska Gov. Sarah Palin has defied political logic with her sudden, stunning announcement to leave office more than a year early.

Supporters and critics alike say the former GOP vice presidential candidate’s resignation, announced Friday afternoon and effective July 26, is an inexplicable move for a high profile Republican widely seen as a contender for a White House run in 2012. A half-term governor campaigning for president?

“If she is thinking that leaving her term 16 months early is going to help her prepare to maybe go on to bigger and better things on the political stage, I think she’s sadly mistaken. You just can’t quit,” said Andrew Halcro, a Palin critic who lost the 2006 gubernatorial race to her.

Palin’s abrupt announcement Friday rattled the Republican Party but left open the possibility of a presidential run. She and her staff are keeping mum on her future plans.

Palin’s spokesman, David Murrow, said the governor didn’t say anything to him about this being her “political finale.”

“She’s looking forward to serving the public outside the governor’s chair,” he said.

And Pam Pryor, a spokeswoman for Palin’s political action committee, said the group continues to accept donations on its Web site, which saw an uptick in contributions Friday afternoon.

The announcement caught even current and former Palin advisers by surprise. Former members of Sen. John McCain’s 2008 presidential campaign team, now dispersed across the country, traded perplexed e-mails and phone calls about the vice presidential nominee’s decision to step down.

In a hastily arranged news conference at her home in Wasilla, a suburb of Anchorage, Palin said she had decided against running for re-election as Alaska’s governor, and believed it was best to leave office even though she had 1.5 years left to her term. Lt. Gov. Sean Parnell will take her place.

“Many just accept that lame duck status, and they hit that road,” Palin said. “They draw a paycheck. They kind of milk it. And I’m not going to put Alaskans through that.”

Palin has proven formidable among the party’s base. But the last week brought a highly critical piece in Vanity Fair magazine, with unnamed campaign aides questioning if Palin was really prepared for the presidency.

The backbiting continued with follow-up articles elsewhere recounting the nasty infighting that plagued her failed bid. Her advisers sniped with other Republicans, underscoring the deeply divided GOP looking for its next standard bearer.

Meghan Stapleton, Palin’s personal spokeswoman, shot down speculation that ranged wildly from Palin dropping out of politics altogether to eyeing runs against fellow Alaska Republicans Rep. Don Young and Sen. Lisa Murkowski. Palin’s comment about serving outside government refers to the present, she said.

Stapleton, however, said it’s too early to say whether Palin would seek the presidency. In the meantime, the governor will continue to work to bring “positive change as a citizen without a title right now,” she said.

“Her vision is what’s best for Alaska, which translates into what’s best for America,” Stapleton said.

Murkowski, whose father was the governor when he lost to Palin in the 2006 Republican primary, was dismissive of the announcement.

“I am deeply disappointed that the governor has decided to abandon the state and her constituents before her term has concluded,” she said in a one-sentence statement.

At the news conference, Palin alluded to how she could help change the country and help military members — an indication that she didn’t think her time on the national stage was over.

On her Twitter page Friday evening, Palin wrote that she was remembering America’s service members on the eve of Fourth of July.

“Thinking of our vets who kept us free & our troops keeping us free today: THANK YOU!” she wrote on the social-networking Web site.

Palin’s decision not to seek re-election is a familiar one for those considering a presidential campaign. Former Massachusetts Gov. Mitt Romney chose not to seek another term as he geared up for an unsuccessful 2008 presidential bid. Minnesota Gov. Tim Pawlenty has announced he won’t seek another term, giving him plenty of free time ahead of a potential 2012 bid. But Romney completed his term and Pawlenty plans to finish his.

Larry Sabato, director of the University of Virginia Center for Politics, said the announcement left many confused. “I think it eliminates her from serious consideration for the presidency in 2012,” he said.

Palin, 45, also has the potential to make far more money in the private sector than the $125,000 or so she has been making as governor. She already had a deal with publisher HarperCollins to produce her memoirs, with publication planned for next spring. Terms of the deal have not been disclosed. Six-figure book deals are common for high-profile political figures.

Palin emerged from relative obscurity nearly a year ago when she was tapped as then Republican presidential candidate McCain’s running mate.

She was a controversial figure from the start and soon became the butt of talk-show jokes. Comedian Tina Fey famously imitated her elaborate updo and folksy “You betcha!” on “Saturday Night Live.”

In Alaska, she saw her popularity wane this year after returning from the presidential campaign. She’s become a polarizing figure, and multiple ethics complaints have been filed against her with the state personnel board.

All but two of the 15 complaints have been dismissed with no findings of wrongdoing, although one complaint led to Palin’s agreement to reimburse the state about $8,100 for costs associated with trips taken with her children. The state says it has spent nearly $300,000 to investigate the complaints, and Palin says she has racked up more than $500,000 in legal fees fighting them.