Transporation Secretary Brock Adams sought a $1.4 billion middle ground between the nation's transit operators and the handicapped community yesterday in his department's new proposal on the costly issue of making subway stations and buses fully accessible for patrons in wheelchairs.

The proposed new rule requires that all new subway stations and buses purchased with federal aid be fully accessible. Beyond that, however, Adams ordered that about onethird of existing inaccessible subway stations be refitted with elevators over the next 12 years or that the transit systems provide alternative service that is "as good or better" than the refitted stations would be.

According to Adams' figures, the costs of the accessibility program for subway stations, trolley terminals, commuter railroad stations, airports and buses would be $1.4 billion over a period of years. That is $800 million less than the original administration estimate of what it would cost.

The biggest issue in an eight-month debate involving Adams, the transit industry and the handicapped community has been what to do about the five big cities that have old subway systems that are almost totally inaccessible to wheelchairs.

Adams' original rule, proposed last June, suggested refitting all inaccessible stations in New York, Boston, Chicago, Cleveland and Philadephia. Those cities joined to say that, at a minimum, it would cost $5 billion to $8 billion. They proposed that only "key stations" be refitted, and Adams seems to have accepted that suggestion.

Within 12 years, Adams said, onethird of existing old stations must be made accessible. Within 30 years, about 40 percent must be made accesible. However, the cities could request waivers from those requirements if they demonstrated an alternative plan providing service "as good or better." If the waiver is granted, 5 percent of the federal operating aid to the big-city transit system involved would have to be devoted to handicapped service.

New rail systems, such as Washington's Metro, have been constructed with elevators for the handicapped and that requirement will continue.

Adams also proposed that, within 10 years, one-half of all transit buses used during the rush hour would have to be accessible to wheelchair users. All buses built since Feb. 15, 1977, have been manufactured so they could be readily equipped with wheelchiar lifts. In Washington Metro's latest bus order, for example, 130 buses were purchased with lifts; another 130 were purchased so that lifts could be added.

Adams' cost estimate does not include the extra price transit authorities will pay for "Transbus," a new, low-floored fully accessible vehicle that Adams has ordered in a seperate rule-making. Bids on the first Transbus contract are to be opened May 3, but both American bus-building firms have said they will not bid.

Th new Adams proposal made public yesterday also requires that commuter rail systems make key stations accessible; that trolley terminals, but not street stops, be made accessible, and that all new cars-whether for subways, communter rail or trolley systems-be fully accessible.

At least one Amtrak station in each metropolitan area and airports that have commercial airline service must also provide handicapped facilities, under the rules.

Adams said that the rules had been difficult for him because "I don't like the position" of having to "weigh the human needs of society against what society can pay." The rules must be reviewed by the Department of Health, Educational and Welfare, but Adams released a letter from HEW Secretary Joseph A. Califano Jr. in which Califano called the plans, "creative and reasonable."

Representatives of the handicapped community, in public hearings last fall, said that full accessibility boiled down to a civil-rights issue. Yesterday Dr. Frank Bowe, executive director of the American Coalition of Citizens with Disabilities Inc., said that, based on his preliminary understanding of Adams' new rule, "we can live with it. We're not interested in a lot of retrofitting," Bowe said, "but we want to get that accessible bus on the street."

Stanley Feinsod of the American Public Transit Association, which fought Adams' earlier rule, said yesterday that "our initial response has to be guardedly optimistic." He cautioned, however, that the wheelchair life was still unproven technology.

Adams released the rules on the same day CBS television had scheduled a price-time news special on the cost of making public facilities accessible to the handicapped, as federal law requires. CAPTION: Picture, BROCK ADAMS . . . offers new proposal