The United States will extend for 30 days its TV Marti broadcasts to Cuba while the president and Congress decide whether the station should remain on the air permanently, the State Department announced yesterday.

The broadcasts, which are made from about 3 a.m. to 6 a.m., have been jammed in Havana after the first few seconds each night, according to State Department spokesman Margaret Tutwiler. "One night it was on for over a minute" before being jammed, she said.

The $7.5 million experiment has "highlighted to the world Cuba's human rights abuses, since they cannot even get simple TV shows," Tutwiler said.

She said by jamming broadcasts of the situation comedy "Kate and Allie," game shows and sports events, Cuba had shown to the world its "fear . . . for their public to have simple information."

A survey of the popularity of TV Marti commissioned for the U.S. Information Agency found that 81 percent of individuals interviewed about TV Marti say they have tried to tune in the station. The study also found that "28 percent of households in the primary target area for TV Marti appear to be able to receive TV Marti, at least occasionally."

The conclusions were drawn from 543 interviews of Cuban tourists, emigres, political refugees and others arriving in Miami.

Granma, the Cuban Communist Party newspaper, called the claim "clearly a lie" in a June 19 editorial and denounced the broadcasts as "illegal" and "internationally repudiated."

The National Association of Broadcasters, one of the principal opponents of the TV Marti experiment, fears that if TV Marti becomes fully operational, Cuban President Fidel Castro will retaliate by jamming radio stations in the United States, as he has done intermittently for years.

"We think it's a boondoggle and waste of taxpayers' money to send a signal over there that Castro is jamming. We hope the public will get the full data on the test when it is completed so people can decide for themselves," Walter Wurfel, a spokesman for the broadcasters, said.

Rep. Bill Alexander (D-Ark.) last Wednesday proposed "a soft approach toward dismantling some of the Cold War bureaucracy . . . offering to cut one-half of the money for TV Marti" in an amendment to an appropriations bill on the House floor.

In floor debate, House Foreign Affairs Committee Chairman Dante B. Fascell (D-Fla.), one of the principal supporters of TV Marti, said, "The Cold War may be over in the mind of the gentleman who is the proponent of this amendment, but it is not over as far as Castro is concerned. . . . If we want to end the elements of the Cold War, continuing to broadcast is the way to do it, not by stopping."

Alexander's amendment to cut the TV Marti appropriation failed, 306 to 111.