On Sunday, Brown dinged Clinton while responding to a Whitman TV ad featuring a 1992 clip of Clinton criticizing Brown.

"I mean Clinton's a nice guy, but whoever said he always told the truth?" Brown said in a speech in Los Angeles.

On Tuesday, Brown said he was "deeply honored" by the endorsement from Clinton, who "after his accomplishment-rich presidency, continues to demonstrate his commitment to bettering our state, our nation, and our world, each and every day."

Brown campaign manager Steve Glazer said further assistance from Clinton, as well as other big-name Democrats such as President Barack Obama, is in the works.

Whitman spokeswoman Andrea Jones Rivera said the Clinton endorsement was no surprise.

Jones Rivera also said Whitman would continue running the ad featuring Clinton, although former CNN reporter Brooks Jackson wrote over the weekend that his 1992 report about Brown's record, which Clinton cites in the clip, had bungled some key facts.

"The fact remains that President Clinton's criticism was correct," Jones Rivera said.

Brown himself cited the Clinton ad to depict Whitman as a liar in the newly unveiled ads, which show Whitman's nose growing like Pinocchio's.

At a press conference in Sacramento, Glazer warned, "We're going to fight back" against what he said was Whitman's "shameful pack of lies."

Later Tuesday, it was Whitman's turn to call for truthfulness in campaigning in letters to TV stations threatening to sue them for slander if they ran a new ad by the California Teachers Association.

The spot accuses Whitman of proposing a $7 billion cut from school budgets and 100,000 teacher layoffs.

"CTA is free to criticize Meg's position on education or any other topic, however, it may not concoct false positions and ascribe them to her," reads the letter from Whitman campaign attorney Thomas Hiltachk.

Comcast spokesman Andrew Johnson said the cable company opted to stop running the ad after receiving the letter. Comcast serves 2 million households from Salinas to Mendocino County.

"We received documentation from attorneys representing both sides," Johnson said. "We reviewed the documentation and after review, our legal team determined the allegations made in the ad could not be substantiated and we pulled the ad."

CTA spokeswoman Sandra Jackson said the ad's claim was based on Whitman's plan to cut $15 billion in state funding overall. She said K-12 and higher education spending make up about half of the state's general fund and typically suffer about half the cuts in difficult budget years.

Hiltachk said in his letter that such a formula is "nonsense" and that education spending is not one of the areas identified by Whitman for cuts.