WASHINGTON - Sarah Palin said on Wednesday that she will not seek the Republican US presidential nomination in 2012, ending months of speculation and leaving the Republican field largely settled.

Palin had left the door open to a run but gave little sign of joining the race to challenge Democratic President Barack Obama. She made it official in a letter to supporters and in an interview with conservative talk radio host Mark Levin.

Former Governor of Alaska Sarah Palin speaks to supporters at a rally organized by the Tea Party of America in Indianola, Iowa September 3, 2011. [Photo/Agencies]

"After much prayer and serious consideration, I have decided that I will not be seeking the 2012 GOP nomination for president of the United States," she said in the letter.

Her decision leaves Republican voters to choose from a field that is led by former Massachusetts governor Mitt Romney, Texas Governor Rick Perry, and businessman Herman Cain, and includes a host of others.

Her announcement came a day after New Jersey Governor Chris Christie opted against running.

"Cinderella's not going to the ball, so Republican voters are going to have to settle for one of her ugly sisters," said Mark McKinnon, a former campaign adviser to Republicans George W. Bush and John McCain.

While most Republicans opposed a presidential bid by Palin, she still has a passionate core following of conservatives and her endorsement would be beneficial.

Perry, a top conservative candidate, quickly issued a statement that could be construed as a bid for her support.

"Sarah Palin is a good friend, a great American and a true patriot. I respect her decision and know she will continue to be a strong voice for conservative values and needed change in Washington," Perry said.

Experts did not believe Palin's supporters would necessarily gravitate toward any one candidate.

"In most polls she was down to single digits. My experience is when you're down to single digits, you split off a percent to this one and 1 or 2 percent to that one. It just doesn't transform the race at all," said Larry Sabato, a University of Virginia political science professor.