SAN FRANCISCO — Many of those at Senator Clinton’s million-dollar fund-raiser with Warren Buffett yesterday left with the understandable impression that the investing guru is giving Mrs. Clinton a hearty endorsement in the hard-fought contest for the Democratic presidential nomination. But, at least officially, he isn’t.

“Why should Hillary Clinton be president of the United States?” he asked at one point during the pair’s hour-long conversation here yesterday. “I won’t vote on the issues. I will vote on — the same way I select a CEO. I’m looking for somebody with the brains and qualities of a CEO,” Mr. Buffett said with Mrs. Clinton sitting at his side.

The crowd of 1,500, each of whom donated between $100 and $2300 to attend, roared with approval. Audience members later told The New York Sun that they thought Mr. Buffett’s endorsement gave Mrs. Clinton a leg up over her Democratic rivals, such as Senator Obama of Illinois.

However, in interviews yesterday, Mr. Buffett reaffirmed his intention to back both Mrs. Clinton and Mr. Obama in the primary contest. While the so-called Oracle of Omaha did a major fundraiser for Mrs. Clinton in New York in June, he also did a somewhat less prolific and less public event for Mr. Obama in Omaha a few weeks later.

As in the June “conversation,” Mr. Buffett did most of the talking yesterday. A main subject was his view that the tax burden falls too heavily on working-class people and not heavily enough on the wealthy.

“My cleaning lady has to pay a higher rate on her income tax than I pay,” Mr. Buffett said, citing the combined effects of income, social security, and Medicare taxes. “It’s better to earn your money in the boardroom than the bathroom,” he said. “If you believe in a trickle-down theory, nothing has trickled since 1987.”

The Berkshire Hathaway chairman said the current mortgage crisis was driven largely by the esoteric and opaque nature of mortgage-backed investment vehicles. “People were buying securities they didn’t understand because there was a little extra yield. More money has been lost reaching for yield than has been lost at the point of a gun,” he said. “Somehow Wall Street started even believing their own baloney on this, and they started holding the stuff.”

After one of Mr. Buffett’s laments about the growing debt America owes abroad, Mrs. Clinton warned that China might try to use its new financial might to discourage America from coming to the defense of Taiwan. The former first lady said a retired general warned her that Beijing could try to blackmail America by threatening to dump dollars “massively” and to cause interest rates here to “go through the roof.”

The shift in the trade deficit and debt held by foreigners “has real world strategic and political implications,” Mrs. Clinton said.

The joint appearance with Mr. Buffett gave the Clinton campaign the opportunity to reach people in finance as well as investing aficionados who might not attend typical political events. The discussion also drew reporters and live coverage from financial news outlets such as CNBC and the new Fox Business Channel.

“I’m a huge Warren Buffett groupie,” a financial adviser from Menlo Park, Calif., John Matthews, said. “I just think it added a lot in terms of credibility to her campaign.”

Mrs. Clinton’s attempt to reach beyond political junkies parallels Senator Obama’s recent foray with Oprah Winfrey, who has the ability to tap into another audience not typically riveted by politics.

One of Mrs. Clinton’s supporters, Mayor Gavin Newsom of San Francisco, suggested to reporters that Mr. Buffett’s imprimatur would be more persuasive than Ms. Winfrey’s tour of early voting states with Mr. Obama. “It’s, candidly, a heck of a lot more important than a celebrity endorsement. This is a guy who knows the issues,” Mr. Newsom said.