Twenty-four of the country’s governors have endorsed a presidential candidate at a time when their support matters most, lending their names, fund raising, and organizing machinery to campaigns desperate for an edge in the primaries.

Among Democrats, Senator Clinton leads with 10 endorsements, including yesterday’s nod from Governor Rendell of Pennsylvania. She also has support from Governors Spitzer of New York and Strickland of Ohio, the state that sealed President Bush’s victory in 2004.

A governor’s endorsement can be campaign gold since governors have a built-in bully pulpit they can use to promote a candidate and their own grassroots organizing and fund-raising networks to share.

Come the general election, it’s natural for governors to support their party’s nominee, and voters take it for granted. That makes governors’ backing particularly important now, in the primary and caucus stage of the campaign. “Voters in the primaries and caucuses are trying to make decisions among candidates that they generally prefer, so those choices tend to be harder,” an Ohio State University political scientist, Paul Beck, said. “There, a governor’s endorsement can be useful.”

The endorsement game started early. A year ago, seven governors already had announced their support for candidates, including Indiana’s Mitch Daniels for Senator, Missouri’s Matt Blunt for Mitt Romney, and Illinois’s Rod Blagojevich for Senator Obama. Despite the jockeying for endorsements, governors’ backing has probably declined in importance over the years, a political scientist at the University of Missouri-Columbia, David Webber, said. That’s due in part to a weakening of state political organizations and in part to today’s information overload, from Web logs to 24-hour news channels.

“People are waiting for [broadcaster] Lou Dobbs to endorse someone,” Mr. Webber said. “I’m not sure governors have as much clout as they did 25 or 40 years ago.”

Mr. Obama has five endorsements, including the support of Massachusetts’s Deval Patrick, the nation’s only black governor and a one-time top official at the Justice Department during the Clinton administration.

On the Republican side, Mr. McCain has four endorsements to Romney’s three. The former Arkansas governor, Michael Huckabee, has support so far from only one governor, Michael Rounds of South Dakota. Governor Perry of Texas is the only governor to endorse Mayor Giuliani.

Some prominent endorsements are missing from governors whose states are among the two dozen that hold primary or caucus contests on February 5, when 1,678 of the 2,025 delegates needed to win the Democratic nomination and 1,038 of the 1,191 delegates need to win the Republican nomination are at stake.

Governor Schwarzenegger of California, the biggest prize on February 5, has yet to back a candidate. He recently said he will endorse eventually, but for now is focusing on the state’s influence in the primary.