California Gov. Arnold Schwarzenegger jumped off the fence Thursday morning in Los Angeles and threw his support behind John McCain, praising the Republican Arizona senator for crusading against wasteful spending and harmful environmental policies.

Schwarzenegger announced his support after touring a Los Angeles-based solar energy company with McCain and Rudy Giuliani, who made good on his pledge to campaign with McCain after dropping out of the presidential race and endorsing him Wednesday evening.

"I am interested in a great future, and I think Senator McCain has proven over and over again that he is reaching across the aisle in order to get things done," Schwarzenegger said. "He's a great American hero and an extraordinary leader -- this is why I'm endorsing him to be the next president of the United States."

The backing could be a big boost for McCain when the delegate-rich state holds its GOP primary Feb. 5, and another setback for rival Mitt Romney.

The endorsement is the latest in a string for McCain, who won the Florida GOP primary after picking up the backing of Florida Sen. Mel Martinez and Florida Gov. Charlie Crist. He also racked up the endorsement of Texas Gov. Rick Perry on Thursday.

Schwarzenegger has been friends with McCain for years but had stopped short of endorsing him while another friend, Giuliani, was also in the race. Schwarzenegger said Thursday that Giuliani's exit from the race nudged him to jump in with his endorsement.

"It's all Rudy's fault," he joked. "Because both of them are friends of mine. This is why I didn't want to endorse anybody."

McCain, a four-term senator, is running strongly ahead of all three rivals in California, which offers a whopping 170 delegates to the Republican nominating convention.

The ultimate effect of Schwarzenegger's endorsement is unclear. The celebrity governor and former actor is universally known in the state, and his political network certainly will be helpful to McCain, who has virtually no organized effort in California after his candidacy nearly collapsed last summer. The actor-turned-governor also is a prolific fundraiser.

But Schwarzenegger has a strained relationship with some conservatives in his own party, and McCain, too, is fighting to convince GOP rank-and-file that he's committed to conservative values. Schwarzenegger's nod could exacerbate concerns about McCain among the party establishment.

Schwarzenegger also is taking heat from state Republicans who argue he's been too willing to bend to the wishes of the Democratic-controlled legislature. At the same time, California faces a $14.5 billion budget deficit over the next year and a half, and the governor has rankled the state's powerful education lobby with his proposal to cut spending by 10 percent from state agencies to deal with the financial crisis.

McCain said Thursday he was honored to field endorsements from Schwarzenegger, Giuliani and officials from all points in the political spectrum.

"You will see a flood of endorsements from across this country from both liberals and conservatives," McCain said.

The Associated Press contributed to this report.