Sarah Palin, the failed 2008 vice-presidential candidate tipped to run for the White House in 2012, has told close friends she is “out of politics, period” after astounding the Republican party with a theatrical resignation as governor of Alaska.

Palin, 45, has found political life demanding with national attention on her family and a steady stream of speculation and allegation compounded by reports that she feared a possible criminal investigation into her relationship with a construction company.

She burst onto the national political scene less than a year ago as the “thriller from Wasilla” — a moose-hunting ice-hockey mom with five children including Trig, a Down’s syndrome baby — and electrified the party’s Christian conservative base as Senator John McCain’s running mate.

In a bizarre, erratic news conference outside her lakeside home on Friday, Palin held out the promise of a national role in politics when she said she hoped to “fight for all our children’s future from outside the governor’s office”.

Yesterday it emerged that she had told “very close friends” she had no intention of running for president. “She is fed up with politics. She doesn’t like her life. She feels that she needs to raise her family,” said Andrea Mitchell, an NBC News reporter who is married to Alan Greenspan, former chairman of the Federal Reserve.

“She really does not want to run for higher office,” Mitchell added. “This is not a case where she is stepping down in order to clear the way for a presidential run.”

As speculation swirled that a scandal was about to break, or that Palin was resigning to further her presidential ambitions, attention switched to her relationship with Spenard Building Supplies, a construction company which sponsors her husband Todd Palin’s snowmobile racing and also supplied the building materials for their home.

Shortly before she became governor, Palin had awarded a contract to SBS to help to build a $13m sports complex in Wasilla, which left the city burdened with debt, according to a report on The Daily Beast website.

Palin’s sudden decision to resign caught some family members by surprise, as well as her bewildered staff and supporters. “She didn’t even tell her brother,” said John Coale, a Washington lawyer and political consultant who is close to the governor. A spokeswoman for Palin said quitting the governorship was a “liberating feeling . . . she can’t get out of there fast enough”.

Friends said she had simply had enough of juggling life in the harsh national spotlight with the increasingly irksome business of running Alaska, six hours’ flying time from the rest of America.

Fred Malek, a Republican ally, was host to Palin and her husband in Washington a few weeks ago. “It was clear to me she was terribly unhappy with the position she was in and the role she was playing,” he said. Malek doubted she would run for president. “I take her at her word,” he added. “I don’t think she’s made any plans in that regard.”

A senior Republican, who knows Palin well, said: “Things had piled up pretty steep on her.” A damaging profile in Vanity Fair magazine this month revealed that some senior aides to McCain were concerned about her mental state and believed she was suffering post-natal depression after she joined the Republican ticket last summer. The article followed a blazing row last month with David Letterman, the late-night television host, who joked after a visit to a baseball game in New York that “during the seventh inning, her daughter was knocked up by Alex Rodriguez”, a Yankees star.

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