Stephen Cutler, who spearheaded the Securities and Exchange Commission’s crackdown on the corporate fraud and trading scandals that rattled American investors following the collapse of Enron, said yesterday that he will resign in a month as the agency’s enforcement chief.

Mr. Cutler, 43, said in a press release that he plans to return to the private sector after six years at the agency. The SEC didn’t announce a successor.

Mr. Cutler and New York Attorney General Eliot Spitzer, sometimes sparring as rivals, together waged an unprecedented attack on business and Wall Street wrongdoing. Mr. Cutler’s aggressiveness also triggered complaints from corporate lobbying groups and critics within the agency itself, who said his enforcement squad was overzealous in bringing cases and pursuing multimillion-dollar fines.

“Steve presided over the agency’s enforcement efforts during a period of the greatest upheaval and challenge since the creation of the SEC,” William McLucas, one of Mr. Cutler’s predecessors, said yesterday in an interview. “His legacy will be in the same category as that of Stanley Sporkin, as one of the greatest leaders and public servants the SEC has ever seen.”

Mr. Sporkin served as the agency’s enforcement chief from 1974 to 1980, before joining the CIA as general counsel and then becoming a federal judge.

Linda Thomsen, 50, Mr. Cutler’s deputy, is the leading candidate to succeed him, securities lawyers said. Ms. Thomsen, who has overseen the SEC’s Enron probe, would be the first woman to serve as enforcement director.

“There’s a strong culture within the enforcement division to promote talent from within,” said Stephen Crimmins, a former SEC trial attorney. “We’ve seen Steve Cutler give Linda a prominent role and she’s proved herself a very capable leader.”

Mr. Cutler, a onetime civil-rights lawyer, is leaving while his 1,300-person unit is pursuing some of its most high-profile cases. Among them are a suit against former Enron head Kenneth Lay, and investigations of alleged bribery by Halliburton.

Mr. Cutler also will be gone by the time the SEC resolves its accounting fraud probe of American International Group and its ousted chief executive, Maurice “Hank” Greenberg.

Mr. Cutler joined the SEC in January 1999 as deputy enforcement director and was promoted to director of the division in October 2001 by Harvey Pitt, the SEC chairman at the time. That month, Enron’s off-balance-sheet financial machinations began to unravel into one of the biggest corporate scandals in American history.

Under Mr. Cutler’s leadership, both the severity of SEC penalties and the number of cases it has brought have set records. The agency levied a record $750 million fine against WorldCom for its 2003 accounting fraud. That compares with a $10 million fine against Xerox in 2002, at the time the highest ever imposed on a company by the SEC.

Mr. Cutler has faced hardening opposition from two of the five SEC commissioners, Republicans Paul Atkins and Cynthia Glassman, who have voted against imposing large fines in some cases. Mr. Atkins and Ms. Glassman voted against a $300 million fine against Time Warner and a $250 million penalty against Qwest Communications International in the past six months.

Mr. Donaldson, a Republican, has sided with the two Democratic commissioners, Roel Campos and Harvey Goldschmid, in backing the fines. The dispute is taking place against the backdrop of a campaign by business groups, including the U.S. Chamber of Commerce, to get the SEC to ease up.

“The pendulum has now swung so far that due process has been put out the window,” Chamber of Commerce President Thomas Donohue said this week.

Mr. Cutler’s next move is unclear. Investment banks and corporate law firms will compete to enlist Mr. Cutler, according to senior partners at two firms in Washington who said they plan to try to recruit him. The two lawyers, who spoke on the condition of anonymity, each said they expect Mr. Cutler may be able to command a compensation package in the range of $3 million to $4 million per year.