Republican presidential candidate Mitt Romney has picked Congressman Paul Ryan as his vice presidential running mate and will announce the pick on Saturday, a Republican official said.

The official, who spoke on condition of anonymity, said Romney would announce Ryan as his choice at an event in Norfolk at about 9 A.M. local time, ending a months-long search for a running mate to face President Barack Obama and Vice President Joe Biden in the Nov. 6 election.

The Romney campaign would not say who Romney has chosen, but he has been working from a short list of candidates that included Ryan, 42, a Wisconsin lawmaker who chairs the House of Representatives Budget Committee, Ohio Senator Rob Portman and former Minnesota Governor Tim Pawlenty.

The running mate would be able to join Romney on at least the start of a four-state bus tour that starts on Saturday at the docked ship USS Wisconsin in Norfolk, goes through North Carolina and Florida and ends on Tuesday in Ohio.

Romney finds himself suddenly falling behind a bit in what has been a razor sharp race with Obama in a campaign that is based largely on the weak U.S. economy.

Ryan's selection, should it happen, would bring a measure of youthful exuberance to the Republican ticket as party activists prepare to gather in Tampa late this month for the convention that will formally nominate Romney as the presidential nominee.

But he would immediately draw attention to a budget plan he proposed as House budget chairman that would include unpopular cuts in government health programs for the elderly and poor.

The conservative Weekly Standard magazine reported that the Romney campaign has begun to prepare a vigorous effort in support of Ryan if he is selected as vice presidential pick -- "something now likely to happen soon."

Often likening Ryan to Ronald Reagan, conservatives say the Wisconsin lawmaker's supposed drawbacks as a candidate - mostly stemming from the steep cuts in social safety net programs he has proposed - are actually strengths that could bring heft, content and perhaps a spark to Romney's campaign.