Legislation designed to sharply curtail the ability of policemen and firemen in the District to retire with full, tax-free disability pensions was approved yesterday by the Senate.

Approval of the legislation, which passed the House in different form last September, comes after disclosure of the uncommonly high proportion of officers who have retired on disability, sometimes decades-old injuries.

Since World War II, every fire chief and all police chiefs but one retired on a disability pension, some of them after being forced from office or denied extensions of duty.

The Senate bill, which passed by unanimous consent, would provide a new flexibility for physicians and the city's retirement board to determine the extent of disability pensions - something that the physicians and city employes on the board have long clamored for.

Another major portion of the Senate bill designed to make the pension fund self-sufficient by the year 2004, would provide $80 million a year in federal funds in each of the next 25 years. The District government would have to match that amount.

The bill passed by the House last September would provide only $42 million in federal funds for city pensions the first year and smaller amounts after that. The House bill's restrictions on disability retirements are essentially the same as those in the Senate bill but would apply only to police and firement hired after the law was enacted.

The House and Senate bills now will go to a conference committee, which will try to resolve these difference in time for final passage before Congress adjourns later this year.

Up to now, the District government has been paying pensions to policemen, firemen, teachers and judges out of the city's annual operating budget. There has been no separate fund of money for the pensions.

As a result the city's current obligation to people in these jobs has spiraled to about $2 billion, leading to predictions of financial disaster from Mayor Walter E. Washington and from the legislative aides who have worked on this bill and the House version.

"If the pension planning continued on a pay-as-you-go basis, then by 1990 the city would pay more in pensions that in active duty salaries - an impossible situation for any city to meet," said Hadley Roff, staff director of the Senate subcommittee on government efficiency and the District of Columbia.

Sen. Thomas F. Eagleton (D-Mo.). chairman of the subcommittee and sponsor of the District of Columbia Pension Reform Act, has said that Congress should help the District meet its pension obligations because Congress had the ultimate responsibility while the system developed.

Mayor Washington said yesterday that the bill was "critically important to the financial integrity of the city's pension system." He said he hopes a bill can be worked out in Congress this session - a prospect that aides familiar with both versions of the bill said was likely.

Under current law, policemen and firemen who are ruled injured in the line of duty by the city's retirement board can collect anywhere from two-thirds to 70 percent of their salaries - tax-free for life - regardless of the severity of their injury.

While some have been genuinely crippled serving the city, other officers and firemen have gone out of full disability for everything from a stiff trigger finger to headaches, from hay fever to alcoholism, from trick knees to back pains that come and go.

As of a few months ago, 82 percent of the District's 2,200 retired policemen and 83 percent of the city's retired firemen were receiving disability pensions. The only police chief since World War II not to retire with a disability pension was Jerry V. Wilson.

The benefits of the disability retirement system in Washington not only exceed those of other cities, but also those awarded in such federal systems as the Veterans Administration, the Civil Service system, Social Security and the Federal Employe's Compensation Act (workmen's compensation).

The bill approved yesterday would allow doctors at the city's police and fire clinics to evaluate severity of injury and make a recommendation of the percentage of disability to the Police and Firemen's Retirement and Relief Board.

That board could then determine for itself the degree of disability, if any, and grant pensions ranging from 30 percent to 70 percent of the applicant's salary. Thus, a man with a damaged kneemight be eligible for only 30 percent of his salary in pension benefits instead of the minimum 66 2/3 percent that he would get now.

The city's current system became the focus of renewed media attention earlier this year when, within the space of two months, chief of police Maurice J. Cullinane left because of complications from a knee injury he sustained a decade earlier, assistant chief of police Tilmon B. O'Bryant retired suddenly with high blood pressure, and five chief Burton Johnson retired on disability because of complications from a knee he hurt 30 years ago.

The House-passed bill, sponsored by Rep. Romano Mazzoli (D-Ky.), would provide the city with $42 million in federal funds the first year and gradually lesser amounts each year after then a total of $741 million over 25 years compared with Eagleton's total of $2 billion.

The House bill also would make the new disability retirement provisions apply to new hirings only. Eagleton's bill would apply to all current policemen and firemen as well as future employes.

Mike Nevens, Mazzoli's administrative aide, and an Ragleton aide met yesterday. Both said they were confident that compromises could be sent to President Carter before the end of this session.