Taking the offensive for the first time in his campaign for governor, Jerry Brown tried to counter Republican momentum by issuing a challenge from the state Democratic convention podium Saturday for his GOP opponents to debate him before the primary election in June.

Brown’s pronouncement, in front of thousands of excited Democrats at the Los Angeles Convention Center, was meant to rally the party against a national tide favoring Republicans that threatens his chances for a second tenure as governor, and has also put Sen. Barbara Boxer in a reelection battle.

He jabbed repeatedly at Republican Meg Whitman, the billionaire former head of EBay who has put $59 million of her own money into her gubernatorial campaign.

“Campaigning and democracy is not about buying hundreds of millions of dollars of 30-second TV ads,” Brown told the delegates, vastly exaggerating her spending. “When we live in a democracy, we’re not consumers of advertising. We’re agents of democratic choice. We’re actors in a historical drama.”

Alluding to commercials aired by Whitman and her fellow Republican Steve Poizner, who trails her in polls for the June 8 primary, Brown said: “Come out from behind those glittering poppy fields, those beautiful car crashes over the mountain. Let’s set up some honest debates.”

Poizner’s campaign immediately accepted Brown’s three-debate proposal; Whitman’s campaign at first said she was open to the idea but later declined.

It was a bit of drama in a convention with little tension among Democrats themselves, because most of the party’s major candidates do not face serious primary challengers.

But beneath their outward enthusiasm while waving signs and handing out stickers for candidates, there was an underlying sense among attendees that they are at a disadvantage in November by virtue of the bruising fight over President Obama’s national healthcare plan and the political pendulum that seems poised to swing against Democrats as the party of power in Washington.

“I need you to be excited -- as excited as the ‘tea party’ people are,” Boxer told Democrats, referring to the Republican-leaning national movement, after she marched into the cheering hall in an outfit of deep coral to “Ain’t No Mountain High Enough.”

“Will you help me?” she asked, and the crowd responded with a roar.

Brown, 72, was governor from 1975 until 1983. His thrifty, nearly invisible campaign has some Democrats nervous about beating the deep-pocketed Whitman, 53. He acknowledged the party’s general unease at the outset of his speech.

“Yeah, there’s some anxiety out there, but we’re on the move, Democrats,” he said. “And I have to say I do feel humbled to be standing before you once again ready to take over the leadership in California. And I’m also really proud to be in a state and a country that chose Barack Obama as our president.”

Although Whitman has yet to win her primary, she loomed large, a kind of boogeyman for Democratic leaders. The state party chairman, John Burton, overlooked Poizner, 53, completely in saying voters have “two choices” in November.

“One is a woman in an empty suit that’s chock-full of money that she wants to spend to buy the governor’s office,” Burton said. “The other is our candidate, a proven commodity.”

State Treasurer Bill Lockyer accused Whitman of an “inability to be truthful” about the level of taxation and spending in the state, among other issues. He criticized her for pushing “a tax break for millionaires and billionaires” and said Democrats needed to defend against “selfish, scaremongering, silly and stupid right-wing ideologies.”

Later, as Brown power-walked between caucuses at the nearby JW Marriott, he told delegates that “your power can make a difference against her money.”

“Running for governor is not like trying to sell a used car with misleading ads on television, bait-and-switch,” he said.

Whitman spokeswoman Sarah Pompei called Brown’s criticism “ridiculous . . . from a guy who hasn’t even been on the campaign trail.” She said he was being propped up by independent expenditure committees that are “union front groups” and had refused to “give Californians any idea where he stands on the issues.”

On the national level, other Democrats signaled that the party would seek to turn passage of the healthcare plan into a referendum on their Republican foes.

U.S. Labor Secretary Hilda Solis said the party would eagerly defend a plan she said gives coverage to 32 million people, requires insurers to cover children with preexisting conditions, helps seniors with prescription costs, allows young adults to stay on their parents’ plans longer and gives tax credits to assist small businesses with coverage.

“Bring it on,” said Solis, who as a congresswoman represented parts of the Eastside and San Gabriel Valley. “I for one know Sen. Barbara Boxer would love to have that discussion with any one of those GOP candidates.”

For the first time, Boxer criticized her Republican rivals, though without naming them. She slammed former Rep. Tom Campbell for his work when he was state budget director, criticized Carly Fiorina for her controversial tenure as chief of Hewlett-Packard and described Orange County Assemblyman Chuck DeVore as an obstructionist.

“One of my opponents was Arnold Schwarzenegger’s top economic advisor during our state’s budget crises. Need I say more about that opponent?” she asked. “Another one of my opponents had a well-crafted and perfectly executed jobs plan . . . for India, for China, for Europe, outsourcing California jobs. A third opponent is a state legislator who’s done nothing to stop the state’s budget mess.”

She told delegates she needed their energy in her reelection battle. “The lines are drawn and, yes, we are in a real fight, a real fight for the direction of our state and our nation,” she said.

michael.rothfeld

@latimes.com

seema.mehta@latimes.com