Mayor Walter E. Washington acknowledged yesterday that District of Columbia policemen and firemen are taking advantage of "the law and the system," to retire in large numbers on disability, and he vowed to do "whatever we can do . . . to modify or tighten the system to make it more workable."

The mayor was careful to avoid labeling the exploitation as abuses. "I can't say the system is abused because the benefits are available by law," he said.

He said that for years he has been concerned about the problems that make it easy for policemen and firemen to retire on disability here, and that annually he has been complaining to Congress, which, he said, is responsible for making corrections.

Eighty-two percent of the District of Columbia's 2,200 retired policemen and 83 percent of the city's 1,000 retired firemen are receiving disability pensions, which are free of income taxes. Every police and fire chief in recent years, with the exception of former city police chief Jerry V. Wilson, has gone out on a disability pension, some of them after being forced from office or denied extensions of duty. Their ailments have included hayfever, alcoholism, a broken wrist, and injuries suffered in a fall from a ladder at home. Many of the retirees then take second jobs, some more demanding than the one from which they retired on disability.

Senators and representatives now studying the system acknowledge that Congress is responsible for it. "Congress built the system -- it was responsible for building the benefits," Sen. Thomas F. Eagleton (D-Mo.), chairman of the Senate Governmental Affairs subcommittee on the District of Columbia, said last week. The system, he explained, was fostered over the years by a Congress more concerned with substituting fringe benefits that would have to be paid "way down the road," than with immediate salary increases.

Congress also was concerned with using pension benefits to recruit a high-quality force of police and firefighters, and saw the disability retirement-system as a way also to properly reward heroes hurt in action, according to city officials.

In spite of the provisions of home rule transferring power to the city, Congress still must deal with reform in this area. The mayor pointed out yesterday that Congress wrote into the home rule bill the provision that the city "will not lessen the rights of employes."

Mayor Washington said the principal reforms he is seeking are included in a bill proposed by Eagleton. Those are:

A partial disability clause that allows doctors and the retirement board to evaluate degrees of disability and award a post on of the applicant's salary depending on the seriousness of the disability. Under the current system, applicants declared disabled are awarded between two-thirds and 70 per cent of their salary depending on the number of years they have served on the forc"

A reduction of the disability pension in response to outside income.

Elimination of the so-called "aggravation" clause that allows injuries sustained off duty to be considered the same as those incurred on duty.

The mayor presented these and other points at a hearing on the bill before Eagleton's subcommittee Thursday. He said yesterday he was gratified to see Congress moving toward change.

The disability retirement system came under increased public scrutiny with the recent retirements of police chief Maurice J. Cullinane fire chief Burton W. Johnson, and assistant police chief Tilmon O'Bryant. All retired with injuries they maintained were incurred in the line of duty.

Asked about his two chiefs, Washington said yesterday he believed they would have qualified for disability retirement even if the system were to be modified by his proposals.