Congressional and public pressure for ending widespread abuses of the District of Columbia's pension program has paid off with a sharp decline in disability retirements by police and firefighters, a congressional hearing was told yesterday.

In 1970 the pension law was so liberally interpreted that 96 percent of the police officers who applied for retirement were granted tax-free disability pensions.

By 1978 that figure had fallen to 51 percent. Last year it plummeted to 22 percent, the lowest in memory, Police Cheif Burtell M. Jefferson told the House D.C. Appropriations subcommittee.

The rate of decline in disability retirements by members of the smaller Fire Department was even greater, falling from 97 percent in 1971 to 16 percent last year, Fire Chief Norman Richardson testified.

Jefferson also testified that the Police Department "is in process of recovering some of the disability payments [already made] because of abuse of the system." He did not cite any figures.

Insp. Isaac Fulwood, the department's budget officer, said one case involved a former officer who hobbled ona cane when appearing before the pension board, but later was photographed carrying two heavy suitcases aboard an airplane.

Other instances, previously cited, included a disabled police retiree who took a laborer's job at a heavy construction site, and another officer, who retired on disability, complaining of a bad back, and then took a job as a school football coach and demonstrated tackling techniques to his students.

After a series of newspaper articles spotlighted the abuses, the D.C. Appropriations subcommittee under its former chairman, Rep. William H. Natcher (D-Ky.), began to tighten budgetary screws on the program.

In 1979, it cut the appropriation for pensions by $10 million, telling the city to adopt reforms. For the current 1980 budget, it cut the appropriation by $5 million.

Jefferson said yesterday that Natcher's chief aim, to bring disability retirements in Washington into line with other cities, virtually has been achieved. He said last year's 22 percent disability retirement figure approached the 15-to-22 percent that is common for other large urban police departments.

William R. Harriston, chairman of the seven-member police and fire-fighters' pension board, said the old high figure on disability retirements stemmed from a "liberal interpretation of the (congressionally enacted) pension law by the board." Such an interpretation ended in large part, he said, because of "prodding by Congress."

Fulwood said the high point in disability retirement came in 1970, when 144 police officers applied to the pension board for optional retirement and 136 -- or 96 percent -- qualified for tax-free disability payments of either 40 or 66 2/3 percent of their salaries.

By 1976, the disability proportion had fallen to 70 percent (75 of 107 retirees). With the abuses spotlighted by publicity and a congressional demand voiced for reforms, the total dropped in 1977 to 61 percent (65 of 106 retirees). Mayor Marion Barry reported last year that the total had fallen even further, to 51 percent (60 of 117 retirees).

Last year's figure of 22 percent disability retirement reflected only 23 individuals among a total of 104 retirees, Jefferson said.

In another matter, Fire Chief Richardson, was questioned at yesterday's Appropriations subcommittee hearing about the city's two-year-old charge for ambulance service. Richardson said only 17 percent of those who are transported to hospitals pay their ambulance bills and much of that comes from Medicaid and Medicare funds.

Based on a charge of $35 per trip, Richardson said the department issued bills last year for nearly $2.5 million, and received payments totaling $378,318. After the costs of hiring five billing clerks were deducted, the net income to the city was $246,170, Richardson said.

"It looks like the city isn't being aggressive enough," Rep. Julian C. Dixon (D-Calif.), the subcommittee chairman, observed.