Updated from 10:10 a.m. EDT

Stephen Cutler, the director of the

Securities and Exchange Commission's

enforcement division who headed the agency's Enron and WorldCom prosecutions, resigned Thursday for personal reasons.

Cutler, who joined the agency in October 2001, will leave his post in a month. He plans to return to the private sector.

"Steve Cutler has been an outstanding leader of the commission's enforcement program," the agency's chairman, William Donaldson, said in a statement. "America's investors have been enormously well-served by Steve's keen intellect, superb judgment and abiding sense of justice.

"He is what every prosecutor should be: tough but fair. We will miss Steve's dedication, leadership and integrity as we continue our critical efforts to pursue and root out wrongdoing in our marketplace."

Cutler's resignation could raise some eyebrows. It comes amid the agency's high-profile probe into accounting at

AIG

(AIG) - Get Report

, the insurance giant.

To be sure, Cutler has had a full plate throughout his tenure, presiding over the largest wave of enforcement cases in the agency's recent history. In each of the last two years, the SEC has collected more than $2 billion in fines.

"This is a real setback to Donaldson's efforts, and he's going to be a hard person to replace," said Mercer Bullard, a former SEC official and currently a securities law professor at the University of Mississippi. Still, Bullard said, "There's no chance that this departure has anything to do with any conflict over the AIG case.

"I'm convinced that Donaldson had been fully behind him, and I think Cutler is probably just tired of the job, which he's been doing for a while now."

SEC enforcement is "about where it needs to be and is producing real results," Cutler said in a speech to corporate directors meeting at Duke University last month.