The Justice Department announced yesterday that Home Dish Only, a New York cable television firm that used an international satellite to beam "adult movies" across the country, had pleaded guilty to felony obscenity charges and will pay $150,000 in fines.

The guilty plea, entered in federal courts in Salt Lake City and Buffalo, N.Y., was the first application of a two-year-old law prohibiting broadcast of obscene programs by satellite and cable stations. Attorney General Dick Thornburgh called it a milestone in the government's efforts to attack "the pollution of the public airwaves with hard-core pornography."

But department officials also acknowledged that the court action would have little practical effect because the cable firm went out of business earlier this year after it was indicted in Alabama on state obscenity charges and satellite stations refused to transmit its films.

The prosecution was the latest by the Justice Department's anti-obscenity section, a special unit with 12 attorneys and a $1.7 million budget that has sharply escalated the government's attack on pornographers this year.

Patrick A. Trueman, chief of the child exploitation and obscenity unit, said yesterday's plea was significant because HDO's two principal officers, Paul L. Klein and Jeffrey Younger, had agreed to "debrief" the government on their contacts with the producers and distributors of the movies they broadcast.

The obscenity unit recently issued subpoenas in Los Angeles as part of a widening probe into the makers of such movies. "We would hope they would be able to tell us who they were dealing with," he said.

HDO began broadcasting "adult" movies in 1986 through a station called American Exxxtasy, which charged about $300 a year to 30,000 subscribers. The firm used U.S. Satellite Inc., an "up-link" facility in Salt Lake City, to transmit the broadcast signal to a satellite, the department said.