"There is somehow the suggestion that because we are having a vigorous debate about who would be the best president, we are going to weaken this party in the fall," he said Sunday at the state Democratic Party convention. "Chill out.
"We're going to win this election if we just chill out and let everybody have their say," Clinton added.
Obama himself said Saturday that the decision about whether to drop out is for Hillary Clinton to make.
"My attitude is Senator Clinton can run as long as she wants," he told reporters in Pennsylvania, where he is campaigning for that state's April 22 primary.
The former president flew in from Pennsylvania to make his pitch at the convention, which attracted a large number of superdelegates, the elected officials and party insiders who will determine whether Hillary Clinton or Obama gets the Democratic presidential nomination.
Nearly one-third of California's 65 named delegates have yet to choose sides. Unlike the pledged delegates won in primaries and caucuses, superdelegates are free to vote for whichever candidate they want.
Of those who have made up their minds in California, Clinton is far ahead, according to a survey by The Associated Press. She has 29 superdelegates to Obama's 13. Twenty-one are undecided or say they will not commit before the party's national convention in August. Two have not responded.
California will have one more delegate when the San Francisco Bay area congressional seat left vacant by the death of Tom Lantos is filled.
Five others will be appointed by the party on May 18, bringing the total to 71.
Clinton delivered a similar message during a private meeting with a couple dozen superdelegates before the speech.
"He talked a little bit about letting the process play out," said Christine Pelosi, an undecided superdelegate from San Francisco who attended and described Clinton as "very good, very intense."
Undecided superdelegates say they see no urgency to make up their minds, despite the campaigns' pleas.
Bob Rankin, an uncommitted superdelegate from Carson, near Long Beach, was still figuring out how to make up his mind.
While Obama leads nationally in the popular vote and in pledged delegates, Clinton won both overwhelmingly in California. Voters in Rankin's congressional district chose Obama, while his congresswoman, Laura Richardson, backed Clinton.
Rankin said Obama called him two weeks ago to urge him to make up his mind.
"He wanted to end this thing now for the good of the party," Rankin said. "I told him I was not ready to do that."
Rankin also received an invitation to attend a private meeting for superdelegates with Bill Clinton at the convention Sunday morning, but turned it down because he planned to leave a day early. He said he'll make up his mind after all the voters have had their say.
"I feel they need to be heard," he said.
