“Maria Shriver is a powerful advocate for Senator Obama,” said Bill Burton, a spokesman for the Obama campaign, in an e-mail message. “We’ll be thrilled to have her campaign for us whenever she can in the coming months. And we remain hopeful that Californians will side with their first lady in November, even if the governor himself does not.”

For his part, the governor, who is negotiating a tremendously difficult budget and other pieces of legislation, is expected to lend a hand to the McCain effort as Election Day draws near. He attends many fund-raisers for Mr. McCain, off the radar, and is desired by a McCain team desperate to draw in the moderate voters that Mr. Schwarzenegger has attracted.

“Arnold Schwarzenegger is a tremendous asset to the Republican party,” said Adam Mendelsohn, an adviser to the McCain campaign and the governor’s former communications director, “especially at a time where there is so much emphasis on independents and disaffected Democrats.”

Ms. Shriver has carefully managed to maintain her professional and political identities since becoming the first lady of California when Mr. Schwarzenegger won the recall election in 2003, reluctantly giving up her job in television news. “Being involved in this administration required me to stretch and to be open minded,” she said.

Like all things Arnold and Maria, the arrangement is far from conventional, but it seems to work.

“Maria called me from Palm Springs one day where she was at a horse show with our daughter and said, ‘I’ve got this thing in my mind that I want to go to U.C.L.A. for Obama, is that O.K. with you?”‘ Mr. Schwarzenegger said. “I said: ‘Do it! You have to do it!’ ”

Ms. Shriver went straight to the airport and hopped on a plane, her hair still a bit mussed from the horse show, and gave a moving speech. “I thought, if Barack Obama was a state, he’d be California,” Ms. Shriver told the roaring crowd. “Diverse. Open. Smart. Independent. Bucks tradition. Innovative. Inspirational. Dreamer. Leader.”

Mr. Schwarzenegger said he felt no compunction about her proclaiming his state for her candidate.

“People get it,” he said. “People know that she is not for Bush even though she is sitting there at the convention with me.”