The FBI is conducting probes of 52 companies that may have illegally backdated stock options and more cases are on the way, its new criminal investigative chief said.

The number of criminal cases has increased 16% in less than two months, said Chip Burrus, an assistant director of the Federal Bureau of Investigation. “We’re going to knock that pretty good,” he said in an interview. “We’re going to go after those.”

Mr. Burrus signaled the Justice Department will oppose efforts to water down the corporate-governance overhaul adopted in the wake of the scandals involving Enron Corp., WorldCom Inc. and others. In the interview, he praised the 2002 Sarbanes-Oxley accounting law, which has been under attack from business groups and Wall Street, and said the FBI is paying close attention to fraud in the $1.2 trillion hedge-fund industry.

The FBI is investigating 486 corporate fraud cases this fiscal year, up from 423 in 2005, according to the agency. It has also opened 1,160 securities fraud probes, compared with 1,139 last year. Twenty of the bureau’s corporate-fraud cases allegedly involve more than $1 billion.

“There is a general idea that this has sort of gone away,” Mr. Burrus said. “It’s not going away.”

The bureau works closely with the Securities and Exchange Commission, U.S. attorneys’ offices, the Justice Department’s fraud section and other agencies.

Mr. Burrus’s comments echo those of Deputy Attorney General Paul McNulty, who said in a June 29 interview that corporate fraud remains a priority for the Justice Department.

Harvey Goldschmid, a former Democratic SEC commissioner, said the rising number of cases involving hedge funds and stock options shows the need for the government to continue opposing business groups’ calls for scaling back corporate regulation.

“There are still serious problems out there,” said Mr. Goldschmid, now a professor at Columbia Law School. “But even more important, there is no basis for dismantling the investor protections contained in Sarbanes-Oxley.”

For executives, Mr. Burrus said, a knock on the door from an FBI agent sends a strong message.

“I’m not interested in civil fines,” he said. “If I’m coming in and I’m looking, there are allegations of criminal misconduct. There’s obviously a different pucker factor that comes when you start talking to an FBI agent.”

Illegal manipulation of stock options is one of the biggest growth areas, Mr. Burrus said. Backdating occurs when companies reward executives by retroactively setting the grant date to a time when the stock was cheap, increasing the potential for profit. At least 130 companies have disclosed internal probes or federal investigations into their options practices.

The first criminal charges in the options scandal were brought against former executives of Brocade Communications Systems Inc, based in San Jose, California, and New York-based Comverse Technology Inc.

Mr. Burrus said the Justice Department is encouraging companies to come forward and admit wrongdoing.

“Honest corporate executives want fast resolution to this so they can move on with what they do best, and that’s the business that they’re in,” he said. “If we linger around these things, then it’s not good for them, it’s not good for us.”

On hedge funds, Mr. Burrus said the FBI is concerned about the number of smaller investors gaining access, mostly through pension funds, to the private partnerships meant for the wealthy. President George W. Bush’s corporate fraud task force, including the FBI, has identified hedge funds as “an emerging threat.”

The assets of largely unregulated hedge funds have more than doubled over the past five years. An attempt by the SEC to set up minimal requirements for the investment pools, such as periodic inspections, was struck down in June by a federal appeals court in Washington.

“It is an emerging threat because of the dollar value and the number of institutions that are actively taking a look at this,” Mr. Burrus said. “People that maybe aren’t expecting to have this type of a risky investment in their portfolio end up taking a bath.”

Several high-profile hedge funds have collapsed in the past two years, including Stamford, Connecticut-based Bayou Management LLC and Atlanta-based International Management Associates LLC, which counted professional football players among its investors. Earlier this month, Greenwich, Connecticut-based Amaranth Advisors LLC informed clients that it lost $6 billion on natural gas trades.

As the Justice Department’s investigative arm, the FBI has some 260 agents working on corporate, securities and commodities fraud cases.

Still, business investigations take a back seat to terrorism and counter-intelligence probes. In Mr. Burrus’s own division, corporate fraud ranks third in importance behind combating gangs and investigating public corruption, he said.

That doesn’t deter Mr. Burrus, 49, who said he “cut his teeth” at the bureau on white-collar criminal investigations in the 1980s and 1990s, especially bank fraud. He joined the FBI in 1983 and rose to head its office in Salt Lake City. Mr. Burrus became acting head of the criminal investigative division in February and was appointed to the permanent job last month by FBI Director Robert Mueller.

“Our goal has always been to maintain the integrity of the markets to protect the average investor,” Mr. Burrus said, citing retirees who “just get fleeced right and left” and those who lose their jobs due to corporate malfeasance.

Mr. Burrus said the agency learned valuable lessons from the accounting scandals, including where to locate resources. Most of the bureau’s financial expertise is in major cities like New York, Los Angeles and San Francisco, and the agency was forced to play “catch up” in places like Clinton, Mississippi, home to WorldCom, and in Houston, where Enron had its headquarters.

“It took us a while to get pedaling on Enron and WorldCom, “Mr. Burrus said.

Karen Spangenberg, chief of the FBI’s financial crimes section in Mr. Burrus’s division, has created four, 10-person regional response teams. They include lawyers, accountants, financial analysts and asset forfeiture specialists. They can be deployed at the first sign of trouble.

“In corporate fraud cases, especially ones that are disintegrating in front of your eyes, there is a real need to quickly get all the evidence,” Mr. Burrus said.

He also said the 2002 Sarbanes-Oxley law, which increased penalties for financial fraud and required executives to certify that their books are in order, “has been a big help.”

The law “brings a seriousness to the company’s financial statements, where corporate executives are held accountable,” Burrus said. “It puts some real teeth into what they knew, when they knew it. And I think it does a great service to the American investor.”