John McCain tapped little-known Alaska Gov. Sarah Palin to be his vice presidential running mate, two senior campaign officials told The Associated Press on Friday.

A formal announcement was expected within a few hours at a campaign rally in swing-state Ohio.

Palin, 44, is a self-styled hockey mom and political reformer who has been governor of her state less than two years.

Palin's selection was a stunning surprise, as McCain passed over many other better known prospects, some of whom had been the subject of intense speculation for weeks or months.

At 44, she is a generation younger that Sen. Joseph Biden of Delaware, who is Barack Obama's running mate on the Democratic ticket.

She is three years Obama's junior, as well ’ and McCain has made much in recent weeks of Obama's relative lack of experience in foreign policy and defense matters.

Palin flew overnight to an airport in Ohio near Dayton, and even as she awaited her formal introduction, close aides said they had believed she was at home in Alaska.

She is a former mayor of Wasilla who became governor of her state in 2006 after ousting a governor of her own party in a primary and then dispatching a former governor in the general election.