Several key Democratic leaders - including the state's two Democratic U.S. senators - lent their less-than-enthusiastic support Tuesday to Republican Gov. Arnold Schwarzenegger's $15 billion bond measure.

U.S. Sens. Dianne Feinstein and Barbara Boxer, legislative leaders and the California Democratic Party announced they are backing Propositions 57 and 58, the governor's twin budget-related measures on the March 2 ballot.

The developments came on the same day the campaign launched a statewide television spot that seeks to reassure voters the measure has bipartisan support. But Democrats were careful not to shower too much praise on the propositions.

"Deficit financing ... is not the best way to do things. But unless you find a very big bank to rob, there is no other way to get this kind of money at this time," said state Senate President Pro Tem John Burton, D-San Francisco.

Assembly Speaker Fabian Núñez and former Assembly Speaker Herb Wesson joined Burton and other Democrats Tuesday to say the bond plan is necessary to spare programs from deeper cuts than already planned in Schwarzenegger's budget.

"These propositions will help the state avert the looming crisis and prevent a similar crisis from developing in the future," Feinstein said in a statement.

State Treasurer Phil Angelides is the only statewide Democratic official to publicly oppose the bond measure and call for a "more balanced approach" to filling California's budget hole.

He said in a statement Tuesday that the bond will "saddle our children and future budgets with debt."

Support from Burton and Núñez, meanwhile, was not surprising because the Democratic-controlled Legislature approved placing the measures on the March 2 ballot.

Support from the state party for the borrowing plan and its companion balanced-budget measure, however, had been less certain. Divided Democratic Party activists failed to agree at their convention last month whether to back the plan, a move that prompted a miffed governor to summon Democratic leaders to a private meeting.

Party members instead agreed to allow Democratic Party Chairman Art Torres to make the final call with input from other party leaders. On Tuesday, Torres said he had reluctantly decided to lend his support.

"It became very clear that this was not the best alternative that we have before us and clearly one that was not the most appealing to us as Democrats," Torres said. "But sometimes in life you have to make hard compromises."

Torres said, however, that party leaders expect Democratic lawmakers to continue to fight for tax increases as a means to balance the state budget, even if the bond measure passes.

"I think there are other answers out there," Torres said.

Torres also challenged Republicans to endorse the bond measure at their upcoming state party convention. But winning widespread support from Republican activists may be a challenge for Schwarzenegger, who already is facing opposition from some conservative GOP lawmakers.

Schwarzenegger spokesman Rob Stutzman said the governor plans to appeal personally to the party faithful in a speech on the first night of the Feb. 20-22 convention in Burlingame.

"That goes against the genetics of some Republicans to endorse a bond. But there is an understanding that this is an inherited problem, this governor was sent here to fix it and at this time, this is the best way to start to work our way out of this deficit," Stutzman said.

If approved by voters, Proposition 57 would allow the state to borrow up to $15 billion to help pay the state's accumulated deficit. Proposition 58, meanwhile, would add a balanced-budget requirement to the state constitution and establish a budget reserve. The measures must pass together to succeed.

"Both of these are good government. They help us move forward," Núñez said. "They help us get a little bit of breathing room so that we can deal with the budget deficit head on."

The governor has been traveling around the state to push the bond measure, which is the backbone of his budget plan. He is scheduled to campaign with agriculture leaders in Tulare today.

Polling last month showed only one-third of voters in support of the bond and at least 40 percent planning to vote it down.

The campaign also unleashed the first of a series of ads that will run statewide supporting the bond measure. The 30-second spot, titled "Duets," features Schwarzenegger and state Controller Steve Westly.