Proposed regulations requiring reconstruction of old subway stations and refitting existing transit vehicles for full access by wheel chairs will cost billions of dollars and return little benefit, the American Transit Associations said yesterday.

APTA, which represents most of the public transit authorities in the United States, estimated that the cost of the regulations as now drafted annually and that such expenditures would divert money from other, more beneficial projects.

Furthermore, APTA chairman James J. McDonough said, even if all existing buses are equipped with wheel chair lifts, even if all old subway stations are refitted with new elevators, even if all commuter train stations are reconstructed with high platforms for easy boarding, "most existing mobility barriers which limit transit use will not be removed . . ."

That is because, McDonough said, 90 percent of the "transportation handicapped" would still have "the inability to get to and from transit stops, the inability to wait out-of-doors, the inability to travel alone or in crowds and the inability to ride while standing."

McDonoush was citing data developed by the U.S. Department of Transportation in a national survey completed in June. His comments here came at the last of a series of five DOT hearings being held across the nation in response to the proposed regulation.

And while McDonough and individual transit authorities attempted to make a case for changing the national rule to one favoring more localized standards, an equally well-organized elderly and handicapped lobby was present yesterday to make its case.

John A. Lancaster, the wheelchair bound advocacy director of the Paralyzed Veterans of America, told the hearing panel that "I resent being unable to use buses and other modes of public transportation merely because I decided to serve my country in time of war."

Full accessibility of transit facilities, Lancaster said, is simply a civil rights issue. "One theme needs reaffirmation," he said, "integration and nondiscrimination. A civil rights issue cannot be decided on the basis of cost effectiveness and local option.

He also said that, as some of the other barriers to mobility by the handicapped were removed or remodeled, such as curbs, "disabled people will be able to get to the bust stops."

William R. Hutton, executive director of the National Council of Senior Citizens, testified in favor of a section of the proposed rule that requires half of all bus fleets to be fully accessible by 1985.

"That requirement is necessary and should remain," Hutton said. "We believe the industry can do it."

Hutton said he had some problems, however, with the concept of wheelchair lifts on buses. Such devices, which lift a wheelchair from the curb to the bus, are now being purchased by some transit authorities, including Washington's Metro. But there have been severe reliability problems. "They're probably unsafe," Hutton said.

Theodore C. Lutz, Metro's general manager, said that eight additional mechanics will have to added just to work on the lifts. About 60 lifts have been delivered to Metro; none has been accepted because of various mechanical problems, Lutz said. "We are committed to having them work properly so we can provide a credible test," Lutz said.

Just last week, DOT issued a final rule requiring all new buses bought with federal aid after September 1979 to have low floors and he equipped with either ramps or lifts for wheelchairs. That kind of bus, called Transbus, received broad support from elderly and handicapped spokesman yesterday.

The biggest cost issue is the refitting of old commuter rail equipment and subway stations.

Peter V. Young of the Southeastern Pennsylvania Transit Authority, which serves Philadelphia should have the option of making some - but not all - stations accessible.

Lutz, in his testimony, posed the central question. 'Will a regulation requiring total accessibility provide real mobility for the vast majority of handicapped citizens or, rather, a somewhat empty symbolic victory?" he asked.