Updated

Former Alaska Gov. Sarah Palin announced Wednesday that she won't enter the 2012 presidential race, making it all but certain that the final slate of GOP candidates has been set.

In a letter to her supporters, the 2008 vice presidential nominee and Fox News contributor said her decision was based on a "review of what common sense conservatives and independents have accomplished, especially over the last year."

"I believe that at this time I can be more effective in a decisive role to help elect other true public servants to office -- from the nation's governors to congressional seats and the presidency," she said.

"I will continue driving the discussion for freedom and free markets, including in the race for president where our candidates must embrace immediate action toward energy independence through domestic resource developments of conventional energy sources, along with renewables," she said.

"We must reduce tax burdens and onerous regulations that kill American industry, and our candidates must always push to minimize government to strengthen and allow the private sector to create jobs."

"I apologize to those who are disappointed in this decision," Palin said during an appearance on "On the Record," with Greta Van Susteren.

Palin's announcement comes one day after New Jersey Gov. Chris Christie affirmed his decision not to jump into the race, despite Republican leaders urging him to reconsider.

After watching Christie announce numerous times that he would not run Palin chose to send a letter over holding a press conference because she wanted to "put the marker down and say 'no I'm not running,'" she said on "On the Record."

Republicans have been searching for an alternative to former Massachusetts Gov. Mitt Romney and were disappointed when Texas Gov. Rick Perry delivered a lackluster performance in the most recent GOP debate.

Romney and Perry remain the front-runners in the race but former pizza company executive Herman Cain has been surging in the polls recently after turning in consistently strong debate performances and winning the Florida straw poll late last month.

"There is not one perfect candidate," Palin said when asked about the current Republican presidential field, adding that voters should not put all of their hope in one individual, and should focus on listening to their ideas and understanding their track records.

A McClatchy-Marist poll showed last month that Palin could have been just as competitive against President Obama as any of the top-tier GOP candidates. In the poll, she trailed the president by just 5 percentage points. The poll also showed Palin doing better than the other candidates, including Perry, who trailed Obama by 9 points, and Minnesota Rep. Michele Bachmann, who trailed by 13 points.

"She is a very important voice," Bachmann said of Palin, during an appearance on "On the Record."

But the poll also showed a large majority of voters did not want her to enter the race, with 72 percent of Republicans and GOP-leaning independents saying she should stay on the sidelines.