Until two weeks ago, Kayla Gillan was deputy chief of staff at the Securities and Exchange Commission, an agency whose duties include policing and regulating the accounting firms that audit public companies. Last week, PricewaterhouseCoopers announced that Gillan was taking a leadership role at the big accounting firm to work on regulatory issues.

Gillan, 52, is just the latest high-profile example of officials moving from the SEC to businesses regulated by it, or to law firms that defend clients in SEC investigations.

From Capitol Hill to academia and the SEC inspector general’s office, observers of the agency have voiced concern that the revolving door can make the SEC a more docile protector of the public interest.

A study to be released Friday by the Project on Government Oversight (POGO), based on hundreds of SEC documents obtained through the Freedom of Information Act, sheds new light on the relationship between the regulators and the regulated.

Over the past five years, 219 former SEC employees filed disclosures with the SEC saying that they planned to represent clients or employers in dealings with the agency, POGO found.

Many of those former SEC employees were appearing before the agency on multiple matters; altogether, they filed almost 800 disclosure statements, the private watchdog group reported.

One former SEC employee, Walter G. Ricciardi, filed 20 disclosures within a two-year period, POGO said. Formerly deputy director of enforcement, Ricciardi is now at the law firm Paul, Weiss, Rifkind, Wharton & Garrison. Neither he nor a spokesman for the firm responded to requests for comment.

The documents obtained by POGO reflect just a portion of the interplay between the agency and its alumni in the private sector. Former employees are required to file such disclosure statements only during the first two years after they leave the SEC.

The matters the former employees were addressing at the agency ranged from SEC enforcement actions to proposed rules for industry and so-called “no action letters,” in which companies seek the SEC’s assurance that something they plan to do will not get them in trouble with the agency.

For example, in March 2006, former SEC official Margaret E. “Mitzi” Moore notified the agency that she had joined the Financial Services Roundtable, which represents big financial companies. Moore wrote that she was scheduled to meet with the SEC’s chairman to discuss, among other things, concerns about a proposal to require disclosures about the salaries of highly paid employees. More than half of the disclosure statements — 403 of 789 — were by people who worked in the SEC’s enforcement division.

The revolving door includes so-called professional accounting fellows, who often come to the agency from big accounting firms and then return to those firms.

“Has the revolving door infected the SEC’s capacity to do its job?” asked Nick Schwellenbach, POGO’s director of investigations. “At a minimum, the revolving door has undermined the integrity of the SEC’s oversight on numerous occasions, and the SEC isn’t policing it as aggressively as it should,” he said.

SEC spokesman John Nester said that while the agency can’t limit the employment of former staff members, they are required to abide by federal restrictions in their new jobs. They can’t represent clients in certain matters in which they played a role at the agency, and some high-level officials must stay away for a one-year “cooling-off” period.

Gillan, who left the SEC too recently to be included in POGO’s study, previously served as one of the leaders of the Public Company Accounting Oversight Board, which Congress created in the aftermath of the Enron and WorldCom accounting frauds to augment SEC oversight of corporate auditors.

“I’m delighted to have the opportunity to help [PricewaterhouseCoopers] as it strives to continually improve audit quality,” she said in a news release.

Company spokesman Steven G. Silber said her role “as envisioned will not require her to spend time before the SEC.”

The SEC’s revolving door factors into pending reviews by the Government Accountability Office and the SEC’s inspector general, H. David Kotz.

In a letter last year, Kotz said he was investigating allegations “that a prominent law firm’s significant ties with the SEC, specifically the prevalence of SEC attorneys leaving the agency to join this particular firm, led to the SEC’s failure to take appropriate actions.” That probe is still open.

In a probe last year of Robert Allen Stanford’s alleged $8 billion fraud, Kotz said an SEC official named Spencer Barasch blocked an investigation of Stanford for seven years. Then, after leaving the SEC, in 2005, Barasch did work for Stanford, the inspector general reported.

“Every lawyer in Texas and beyond is going to get rich over this case. Okay? And I hated being on the sidelines,”Barasch said, according to the report.

An SEC ethics official concluded Barasch was prohibited from representing Stanford, the report said.

In a statement Thursday, the managing partner of the law firm where Barasch now works said the firm believes he acted properly.

“He did not violate conflicts of interest,” Bob Jewell of the firm Andrews Kurth said.

Staff researcher Magda Jean-Louis contributed to this report.