A federal judge in Philadelphia has issued an opinion ordering public transit authorities across the country to provide service to the handicapped, no matter the cost.

The Monday order by U.S. District Court Judge Marvin Katz strikes down a 1986 Department of Transportation regulation that required authorities to provide services to disabled persons but allowed them to limit expenditures on those services to 3 percent of their operating budgets.

According to the ruling, the transit industry "may be permitted to take the least expensive or most cost-effective route toward providing services to their disabled patrons, but those services must in fact be provided. The cost limit at issue here permits the burden of cost to eviscerate the civil right."

Tim Cook of the Public Interest Law Center of Philadelphia, one of the attorneys representing the plaintiffs in the case, said the ruling will affect "millions of riders" and "every transportation authority in the country." The case was brought on behalf of 17 disabled groups, including Americans Disabled for Accessible Public Transportation, which has chapters in 25 U.S. cities.

Cook said the case is part of a broad movement by advocates for the disabled to enforce for the handicapped civil rights guarantees for the use of all public facilities.

Katz called the 3 percent ceiling "arbitrary and capricious" and said it denied handicapped individuals "the minimum quality of service mandated by the Congress."

He upheld DOT regulations giving transit authorities six years to implement a system fully accessible to the handicapped and stayed his decision for 30 days to give the federal government a chance to appeal.

Robert S. Marx, a spokesman for the Transportation Department, said yesterday he could not comment because he has not yet seen a copy of the opinion.

Cook said the case was brought by handicapped transit riders whose travels were heavily restricted because many cities do not have readily available buses or rail systems adapted to accommodate the handicapped.

"In many cities, the only way a handicapped person can get a ride on public transportation is to call at least a week ahead and make a reservation . . . I don't usually know a week ahead of time what my plans will be," Cook said.

He said some of the worst transit systems for handicapped persons are in older cities such as Philadelphia, Baltimore, Cleveland, Chicago and Kansas City.

He said the District of Columbia and New York City are somewhat accessible, while Seattle and Denver transportation systems are easily accessible to the handicapped.

Mary Bucklew, a spokeswoman for Washington's Metro system, said yesterday that the agency's legal staff has not had a chance to evaluate the ruling.

"But Metro is and has been meeting and exceeding DOT requirements," she said. Bucklew said all Metrorail stations are accessible by elevator and about 26 percent of buses are equipped with lifts for wheelchairs.

"Our goal is for 50 percent of all buses to be lift-equipped," she said. She said a number of bus routes are served by lift-equipped buses, and any handicapped passenger can arrange to have a lift-equipped bus on a specific run by calling 24 hours ahead. She said problems arise if the handicapped passenger is late and misses the special bus.

Bob Previda, of the New York Transit Authority, said it was too early to tell what the order will mean. But he said the city, as the result of an earlier consent decree, is in the process of retrofitting major subway stations with handicapped access at a cost of about $60 million. "We won't do it citywide because it's so costly," he said, adding that gaps in the system will be filled by vans equipped for handicapped passengers.

John Cunningham, of the umbrella New York Metropolitan Transit Authority, said that about 75 percent of the New York bus fleet is equipped with lifts and the entire fleet is expected to be equipped by the early 1990s.

Katz stopped short of ordering each transit system to supply enough lift-equipped buses to serve all disabled riders. But Cook said the decision will force systems to move in that direction because lift-equipped buses are cheaper to use than vans that provide door-to-door service for the handicapped.