NEW YORK, May 4 (Reuters) - A 67-year-old attorney has sued his former firm, Frenkel, Lambert, Weiss, Weisman & Gordon for age discrimination, underscoring a persistent problem for law firms as they confront a graying corps of baby boomers.

Former associate Stephen Marcus's complaint in Manhattan federal court alleges partners pressured him to accept a 50 percent pay cut in August 2009 before terminating his employment three months later after two decades at the firm.

"It's a problem for the profession," said Mark Alcott, a former New York State Bar president who created a committee to study the issue of age discrimination during his tenure.

Although not an issue in Marcus's case, some firms have mandatory retirement policies.

"We have large numbers of lawyers who are entering their 60s, progressing through their 60s, and they're retiring -- many by choice, some because they run afoul of these policies, and it's leaving a void," Alcott said.

Calls to Frenkel, Lambert seeking comment were not returned. The lawyer representing the firm, John Porta of Jackson Lewis, was unavailable for comment.

In 2007, Alcott's committee issued recommendations, later adopted by the state bar association, that law firms end mandatory retirement policies for partners. The American Bar Association followed suit the same year.

While some firms elected to do just that, a number have continued to enforce retirement ages, even as a sizable cohort of lawyers reaches senior citizen status. Alcott said such rules are rarely enforced in other industries.

The policies are limited to partners, not associates, and rely on the argument that partners are employers rather than employees and thus are not entitled to the same level of protection under anti-age discrimination laws.

PRACTICING LAWYERS OLDER

Nevertheless, the Equal Employment Opportunity Commission filed suit against Kelley, Drye & Warren last year on behalf of Eugene D'Ablemont, a partner forced to give up his equity when he hit age 70. The case remains unresolved.

In 2007, Chicago-based firm Sidley Austin settled a similar lawsuit from the EEOC for $27.5 million, a case that signaled to other firms with retirement policies that they could be vulnerable, Alcott said.

Jeffrey Burstein, the EEOC lawyer handling the Kelley Drye case, said the commission chooses its cases carefully.

"Certainly the number of lawyers who currently are practicing or want to practice past ages that previously had been considered retirement ages has been growing," he said. "I think that's pretty clear."

Only a tiny fraction of age discrimination complaints filed with the EEOC in 2010 were aimed at law firms, according to the agency's statistics. Of 878 complaints filed in New York State, just three named law firms; nationally, 39 of 23,264 complaints were filed against law firms.

Unlike the plaintiffs in the EEOC lawsuits, Marcus was not a partner.

In addition to age discrimination, the filing alleges that the firm committed fraud by telling Marcus that there weren't enough profitable cases available in his area of expertise.

"Frenkel, Lambert's decision forcing Marcus to take a reduction in pay -- all the while saying that higher paying work was not available -- was simply a pretext for age discrimination," the suit states.

Marcus's lawyer, Neal Brickman, said Tuesday that the firm had targeted Marcus because of his age and his paycheck.

The case is Stephen H. Marcus v. Frenkel, Lambert, Weiss, Weisman & Gordon, LLP, et al, United States District Court, Southern District of New York, No. 1:11-cv-02905.

For Stephen Marcus: Richard Jefferson and Neal Brickman.

For Frenkel, Lambert: John Porta of Jackson Lewis.

(Reporting by Joseph Ax; Editing by Howard Goller)