The federal Communications Commission voted yesterday for a major, nationwide expansion of AM radio stations by limiting the interference protection granted powerful nighttime broadcasters.

The commission's decision to limit "clear-channel" broadcasters is expected to create as many as 125 new AM stations.

Initially, the action is expected to benefit small communities with local radio service. In addition, the new rule is aimed at cities with substantial minority populations that either have no minority-owned stations or are considered by the commission to be underserved by minority-owned stations.

Commission members also said that additional stations are expected to be used to provide public radio in areas now only served by commercial stations.

The FCC listed 37 communities likely to qualify for new stations under it guidelines, none in the Washington metropolitan area, Whether the guidelines eventually might allow for additional stations in this area is unclear.

FCC officials said they expect as many as 2,000 applications for the newly available frequencies, the first major expansion of AM stations in many years.

What the commission did to make additional frequencies available for new AM stations was to modify regulations protecting powerful "clear-channel" stations, which were previously assured transcontinental protection from interference at night.

Instead, the FCC voted to limit protection to 750 miles in any direction form the stations. Reception beyond 700 miles has been unreliable even under the old standards, FCC chairman Charles D. Ferris said.

"By protecting the 25 clear-channel stations from interference across a diameter of 1,400 to 1,500 miles, most people who now listen to 'skywave' broadcasts will continue to hear them," Ferris said.

For instance, many listeners to the Grand Ole Opry broadcast on a Nashville clear-channel station, will continue to receive the Opry without interference. Signals from the 50,000-watt, clear-channel stations have been received infrequently beyond a radius of 750 miles when atmospheric conditions were correct.

The clear-channel stations were established decades ago on channels on the AM dial to provide service to listeners in rural areas with no local radio service.

Ferris called the FCC decision a "compromise that will satisfy dual needs" by maintaining the benefit of broad nighttime coverage on the clear channel stations while opening an opportunity for more service elsewhere.

Ferris also said that if the United States had failed to place additional stations on clear-channel frequencies along U.S. borders, it might have lost rights to interference protections along those frontiers.

Only one Maryland or Virginia community -- Collinsville, Va., outside of Martinsville in the southwestern part of the state -- made the FCC's initial list of communities that may pick up a new AM station. Colinsville was listed among communities without local radio service.

In other action yesterday, the FCC approved a tariff setting price for Comsat, the public-private communications satellite company, to provide service directly to television networks. Previously Comsat could provide satellite service only through international record carriers such as At&t.

What the FCC did was to allow Comsat to provide the service directly at the same costs charged by the international record carriers.