Poland's suspended Solidarity trade union scored a major propaganda success tonight by inaugurating its own pirate radio station with a call for further resistance to martial law.

The 10-minute broadcast began with a popular song sung by Polish resistance fighters in World War II and included an antigovernment song and protests about conditions in internment camps. It was clearly audible in large parts of Warsaw on an FM wavelength, according to monitors. It ended with an appeal to Warsaw residents to switch off their lights between 9 and 9:15 Tuesday evening, exactly four months since the military crackdown.

"This is Radio Solidarity," a man's voice said at the beginning of the program, which was described as "a trial broadcast to test our technical equipment." It was believed to be the first such pirate radio station to operate in the Soviet Bloc since the invasion of Czechoslovakia in 1968.

For the past few weeks, pamphlets have been circulating in Warsaw announcing the broadcast, and discreet notices were pinned up in several churches on Easter Sunday. But few Poles actually believed that Solidarity would succeed in launching the station in view of the government's rigid controls over the mass media.

Until now, underground Solidarity activity has consisted mainly of the distribution of clandestine information bulletins in universities, factories, and buses. Several hundred such bulletins, ranging from well-produced offset newsletters to typewritten sheets, are believed to be in circulation in Poland.

The fact that Solidarity now has managed to break the official monopoly of the airwaves is likely to give a psychological boost to the union's supporters. It also can be expected to cause considerable embarrassment to the government, which resisted Solidarity's demands for access to radio and television even before the introduction of martial law.

Radio Solidarity was launched precisely as advertised: at 9 p.m. on 70.1 megahertz, halfway between Radio Warsaw's second and fourth programs. The pirate station chose as its call sign the tune of a popular song sung by Polish resistance fighters during the Nazi occupation.

The two announcers, a man and a woman, asked their listeners to record the program on cassettes to check the authenticity of future broadcasts. They said they would be presenting future programs together "if God allows, to victory and until our radio station will cease to be needed."

Listeners were invited to join in a survey of audibility, with households blinking their lights three times for very good reception, twice for good and once for adequate. Observers were said to be stationed in different parts of the city to note the results.

In several Warsaw suburbs, lights in apartment blocs reportedly were flashed on and off during the broadcast. Audibility varied from good in the city center to poor on the outskirts, but there was no evidence of interference or jamming by the authorities.

Experts said that the technical aspects of launching the radio station probably would have been relatively simple, with the use of equipment costing less than $200. It is extremely difficult for the authorities to detect precisely the source of an illegal FM broadcast lasting less than 15 minutes.

Radio Solidarity announced that its next broadcast would take place at 9 p.m. April 30, and listeners would then be informed about a series of regular programs.

The inauguration of the station was carefully timed for the last day of the Easter holidays, a family occasion for many Poles. Before the broadcast, many people in the city of 1.5 million said they would try to listen in.

One of the announcers said that "many families gathered around their holiday table have forgotten that we are living in a country at war, a war declared by the authorities against their own nation. This war has claimed victims and is still claiming them."

The announcer paid tribute to miners killed during clashes with riot police at the Wujek coal mine in the southern city of Katowice last December. He said that inmates still are beaten in internment camps where nearly 4,000 Solidarity activists are still being held.

One student at the Catholic University of Lublin had been beaten so badly that his spine was broken, the radio announcer said.

"Let us remember this when they say that life is normalizing. There can't be normalization in a country where people are beaten and imprisoned, where human rights are being stamped upon.