LOS ANGELES – Mayor Hahn’s reelection bid has suffered – along with the image of honesty he worked hard to cultivate – amid accusations he let corruption and fraud flourish at City Hall.

County prosecutors have been investigating allegations that Mr. Hahn’s supporters shook down companies that wanted to do business with the city by tying public contracts to political contributions.

Federal prosecutors have opened their own inquiry.

Mr. Hahn has not been implicated and denies knowledge of any potential wrongdoing, but the investigations touch whole segments of city government – from members of Mr. Hahn’s inner circle to Los Angeles International Airport and the water and power department.

No city official has been charged, though several have resigned.

But with prosecutors issuing subpoenas for Mr. Hahn’s office e-mail and summoning some of his aides before grand juries, the investigations have become a popular topic for his four main challengers in the March 8 primary.

“He’s the piñata. The question is the whether the pinata will survive,” said Robert Stern, president of the nonpartisan Center for Governmental Studies at Santa Monica.

Critics have cast Mr. Hahn’s administration as the most corrupt since a scandal-plagued mayor was recalled nearly 70 years ago, and some of his supporters have gone so far as to withdraw their endorsements.

“It’s more than a scandal. It’s crippled his administration,” said Councilman Bernard Parks, a former police chief whose ouster was backed by Mr. Hahn and who is one of the mayoral candidates.

Mr. Hahn has been reminding voters of his reputation for personal integrity.

“There’s no factual basis for any of these charges,” said Mr. Hahn’s campaign consultant Kam Kuwata. “It’s always rhetoric and hot air.”

However, more than a third of respondents to a Los Angeles Times poll said Mr. Hahn lacks the honesty and integrity to be mayor.

The poll also found that none of the five candidates appears to have the majority support needed to avoid a May 17 runoff. The race is nonpartisan, and all five major candidates are Democrats.

The investigations accelerated following an audit by Los Angeles’ public watchdog, the city controller, that said shoddy records and meddling by political appointees in screening airport contracts gave the appearance of conflicts of interest and abuse.

Separate audits criticized the secretive process by which the harbor department awarded leases and accused a publicity firm of overcharging the city’s water and power agency by millions of dollars.

Local and federal prosecutors largely have refused to comment.

“It does damage the city’s reputation,” Xandra Kayden, senior fellow at the University of California, Los Angeles, School of Public Affairs, said of the charges of corruption. “This isn’t Tammany Hall corruption, but it’s a major loss of credibility.”