Judging from testimony at a series of Metro board hearings, many Washingtonians are more worried about possible deterioration of bus service thatn the threat of higher fares on July 1 when the subway system is expanded.

Several witnesses also predicted that few District residents will bother to transfer from buses to trains at higher costs to get to and from downtown.

"Since most . . . residential areas in D.C. will have reasonable bus service . . . competing with Metrorail, it is unlikely that any of these bus riders will switch to the subway," Kenneth U. Mowill, a spokesman for the D.C. Statehood Party, told one hearing.

Mowll predicted this "will result in a largely segregated transit system, with the poor and black squeezed into sweltering buses while the rich and white use the fancy new suburban railroad (the Metro subway)."

Basically at issue in a series of six city and suburban hearings that concluded last night was the method for transferring between the bus and rail systems starting July 1, and the fares to be charged. For District residents, the fares would be invariably higher the for all-bus trips.

Also under consideration is a proposed increase of the District Metro-bus fare in rush hours from 40 cents to 40 cents in an attempt to reduce the system's deficit.

At hearings last week in Silver Spring and at Lincoln Junior High School in Northwest Washington's Mt. Pleasant neighborhood, District residents worried out loud that the extension of the subway would cause service to deteriorate on existing bus lines.

Most changes would occur July 1, when the second rail line is opened from Stadium-Armory station through downtown to National Airport station in Arlington. A second extension is tentatively scheduled for Nov. 1, from the Rhode Island Avenue terminal of the existing downtown line to Silver Spring station.

Daniel J. Yurman, speaking for citizen groups in the Adams-Morgan district, centered on 18th Street and Columbia Road NW, said the proposed fare structure "is tied to a plan which will lower the level of bus service available in our neighborhood."

The plan he cited would eliminate service from Union Station to Mt. Pleasant on the No. 40 bus line at hours the subway is operating, leaving the Mt. Pleasant end of the line served on by No. 42 buses and by a [WORD ILLEGIBLE] No. 46 line that would go to Foggy Delham instead of downtown.

Already, Yurman said, Metro bus eliminated several buses in the morning rush hour, causing sever over-crowding. He said he protested the cuts in a letter to Theodore C. Lutz, Metro's general manager, and Lutz replied that "the cuts in service were testified and residents of your neighborhood have not been inconvenienced as a result."

It was, Yurman said, "an absolutely incredible answer."

Yurman said inner-city residents "are opposed to paying increased fares during the rush hours in return for decreased service."

Several residents of Shepherd Park, a neighborhood wedged between the Walter Reed Army Hospital and the District-Montgomery County line, testified in similar vein at the session in Silver Spring.

One witness expressed concern that service on the frequently operated 16th Street and Georgia Avenue bus lines will be curtailed because much of their financial support would be diverted to the Silver Spring rail lin after it opnes next November.

Charles N. Mason Jr., who lives in that neighborhood, said residents like himself would be put at a severe financial disadvantage by riding by Metro-rail system.

Under Metro's proposal, Mason said he would have to pay an interstate bus fare to get to the closest rail station to his home at Silver Spring, and a fare calculated on travel distance to get downtown. This would produce a one-way fare in rush hours of $1.80 to one typical downtown station, compared with 40 cents now and a proposed 50 cents by bus.

The turnout at all the hearings was small compared with similar hearings prior to 1973, when the bus system was owned by a private corporation.

Raymond Fisher, testifying Monday night at Ballou High School for the Naylor-Dupong Community Assembly, a Southeast Washington group, said he interviewed people at bus stops and got a troublesome answer.

"Everyone I interviewed felt the fares would be increased and they could do nothing about it," Fisher said.