One of the most persistent critics of the District of Columbia's disability pension program, James R. Mandish, has retired as an assistant director of the D.C. personnel office - on a disability pension.

His former boss, D.C. personnel director George R. Harrod, said the 37-year-old Mandish complained of persistent severe chest pains and once nearly collapsed at the office, and had to be taken to a hospital.

"The doctor told him point blank that he would have to give up his job," Harrod said.

Mandish will receive 40 percent of his salary of about $38,000, a figure based on 15 years of governemnt service, and must pay income taxes on it.

Harrod said Mandish has applied for - but not yet received - tax-free benefits under a law that permits compensation for work-related disorders suffered by federal and D.C. workers.

Officials of police and firefighters unions chided Mandish for seeking and accepting disability benefits after repeatedly criticizing alleged abuses in the retirement system that serves their members.

"Jim was a severe critic of our system, and I do think it is ironic that he would go on disability," said David A. Ryan, President of the D.C. Fire Fighters Association. "But a disability is a disability, and he is entitled to whatever his system provides."

Alan Whitney, executive vice president of the International Brotherhood of Police Officers, said it was "strange that the one who has given us the most grief (on disability pensions) is availing himself of a very similar benefit."

Harrod defended Mandish, who left Thursday for a vacation in New York state and could not be contacted. Harrod said Mandish wanted to close costly loopholes that, a few years ago, permitted 98 percent of all retiring police officers to go out on tax-free disability. Last year, the figure was down to 55 percent.

The issue flared anew early this year when three high-ranking officers - former fire chief Burton W. Johnson, former police chief Maurice J. Cullinane and former assistant police chief Tilmon O'Bryant - retired on full disability in quick succession after long, active careers.

The House D.C. Appropriations Subcommittee recently voted to trim the city's proposed police and firefighters' retirement fund of $64.6 million next year by $10 million in an attempt to force the adoption of tighter restrictions.

Under a D.C. law passed by Congress, tax-free pension benefits are available only to police and firefighters who are determined by doctors and a retirement board to be disabled. Those who are found to be physically fit pay taxes on their pensions.

Harrod said pension benefits paid to civilians, such as Mandish, are taxable under the provisions of other laws.

There are no degrees of disability for a retiring police officer or fire-fighter. He is judged either to be disabled or physically fit. In the case of former police chief Cullinane, the disability was a knee injury suffered during a demonstration in 1969, eight years before his retirement.

Mandish recently assisted a House District subcommittee in writing a proposed new pension law that, among other things, provides for partial disability with scaled-down benefits for police and firefighters with marginal injuries. The measure has passed the House and a different version is awaiting Senate action.

In addition to his work on pensions Mandish monitored unemployment compensation programs and was on a team that negotiated with police, firefighters, sanitation and teachers unions on wages and benefits.

Harrod said the hard-driving Mandish suffered chest pains and became short of breath at a staff meeting in April. He was taken to Holy Cross Hospital in Silver Spring for treatment by his family physician, who diagnosed severe muscle spasms.

Harrod said he offered Mandish another job "but the doctor said he had to be out of this environment entirely." His retirement took effect June 22.

James O. Moran, who succeeded Mandish said the job "is very pressure-demanding." He said "it had been rather obvious for some time" that Mandish was headed for a physical crisis.