Updated: 8:38 p.m.

Former Alaska Gov. Sarah Palin will not be running for the Republican presidential nomination, she informed supporters in a letter tonight.

“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 wrote in the letter, which was reported by ABC News and which she posted as a note on her Facebook account later in the evening.

The window for a Palin campaign was rapidly closing because of impending primary filing deadlines, but she refused to rule out the possibility until today. In the past few months, she appeared at the Iowa State Fair during the Ames straw poll, has released political-ad-style Web videos and has made numerous ambiguous comments on the topic.

She told Fox News last week: “Through my process of decision-making with my family and with my close friends as to whether I should throw my name in the hat for the GOP nomination or not for 2012 — is a title worth it? Does a title shackle a person?” 

She added, “Are they someone like me, who’s a maverick — you know, I do go rogue and I call it like I see it, and I don’t mind stirring it up in order to get people to think and debate aggressively, and to find solutions to or the problems that our country is facing.”

Joshua Miller contributed to this report.