WARSAW, May 9-A clandestine radio station of Poland's suspended Solidarity trade union managed tonight to broadcast a brief appeal for a 15-minute general strike on Thursday before being drowned out by government jamming.

The call for the strike, to mark five months of martial law, was made in the names of four underground Solidarity leaders from Warsaw who avoided arrest in the military takeover Dec. 13. Appeals for similar strikes have been made in other parts of the country.

If it goes ahead, the protest is likely to prove a key test for the Communist authorities because it would be the first coordinated nationwide strike since the first days of martial law last December. Last week pro-Solidarity street demonstrations in many cities were broken up by riot police using tear gas and water cannons.

Earlier today, the government mounted a show of force in Warsaw following an official parade to celebrate the anniversary of the end of World War II in Europe. Thousands of police patrolled streets in the old part of the city, checking identities of young people and arresting some.

Tonight's broadcast by Radio Solidarity lasted just 45 seconds. But despite its brief duration, it demonstrated that the authorities still have not succeeded in silencing the station despite an intensive police effort to find the transmitter.

The broadcast began with a popular song from the days of Nazi occupation, the same signature tune used for the inaugural broadcast April 12. The announcers, also the same as April 12, then read what they described as an appeal by Solidarity's regional executive committee for Warsaw headed by Zbigniew Bujak.

The message called on workers in Warsaw factories to join Solidarity branches elsewhere in a 15-minute protest starting at noon Thursday. Motorists were asked to stop for one minute and sound their horns in protest.

At this point, the voice of the Radio Solidarity announcer was lost beneath loud pop music that continued for the next hour.

The authorities appear to have chosen jamming as the best tactic for dealing with the radio station following the failure of a big police search April 30. According to underground Solidarity bulletins, special radio detection equipment was brought in from the Soviet Union and East Germany to try to trace the broadcasts. But despite house-to-house searches and the cordoning off of large parts of Warsaw, nothing was found.

Solidarity activists said that an abrupt interruption in the middle of the April 30 broadcast was caused by equipment failure. A third broadcast on May 3, the night of serious rioting in Warsaw, was inaudible because of interference.

The police action in Warsaw today came after hundreds of people sang religious hymns while gathered around a cross of flowers in the middle of Victory Square. The cross, in honor of the late primate of Poland, Cardinal Stefan Wyszynski, has become part of a battle of wills between the authorities and Solidarity supporters.

It was removed on the eve of official May Day celebrations last week and again today before a big Victory Day march. Within moments of the end of the parades, however, young people had reconstructed it.

This afternoon, a crowd surrounded the cross and refused to move on despite the appearance of hundreds of police trucks, jeeps mounted with tear-gas launchers and an armored personnel carrier. A thunderstorm finally caused the crowd to disperse, and police then cordoned off the area.