In a surprise move, Alaska Governor Sarah Palin said on Saturday she was stepping down and would not seek re-election, fuelling swift speculation of a possible 2012 White House bid.

Palin, who was Republican John McCain's controversial running mate in his failed 2008 White House bid, said she would step aside as governor in "another few weeks" and be replaced by Lieutenant Governor Sean Parnell at the governor's picnic in Fairbanks, Alaska on July 26.

Palin, 45, told a press conference at her lakefront home in Wasilla, Alaska, that she wanted to "take a stand and effect change, not just hit our head against the wall and watch valuable state time and money."

In leaving her post before the end of her first term, Palin will be able to travel across the country more freely and build up a national political team, clearing the way for a potential presidential bid of her own.

A June 2 TV channel poll had Palin running neck-and-neck with former Massachusetts governor Mitt Romney and ex-Arkansas governor Mick Huckabee in the top three favorites to head up the Republican 2012 ticket.

But shooting down any speculation her announcement was abrupt, Palin said: "Some are going to question the timing of this, and let me say this decision has been in the works for quite a while."