Solidarity leaders launched a strike Monday in the giant Lenin shipyard, birthplace of the independent trade union, igniting strikes across Poland in the worst crisis since the imposition of martial law in December 1981.

About two hours after the day shift began, about 800 workers hung a huge "Solidarity" banner outside the shipyard's Gate No. 2 and announced, "We have begun." Then about 300 marched toward the main gate chanting, "There is no freedom without Solidarity."Riot police with special battle batons and backed up by tear gas launchers surrounded the Lenin shipyard, where about 7,000 to 8,000 workers had reported on the day shift, and cleared the area near the main gate entrance, refusing entry to everyone.

It was not known how many workers were involved in the strike at the shipyard, where about 10,000 workers are employed.

"The Lenin shipyard is on strike," declared local strike leader Alojzy Szablewski. "The only demand is the re-legalization of Solidarity."

Within hours of the strike, thousands of workers in several other plants across Poland joined the strike.

In Poznan, scene of bloody 1956 riots in which scores of workers were killed, several thousand workers struck at the Cgielski ship engine plant, while 1,200 went on strike in the huge Stolowa Wola steel works in the southeast, activist sources said.

Most of the 4,500 employees at the port of Gdansk, and 1,000 at a railway equipment parts firm in Szczecin, also went on strike.

In Warsaw, one department that struck in the huge Ursus tractor plant was surrounded by police, activists said, and former Ursus employee and regional Solidarity leader Zbigniew Janas was detained.

Activist sources said about 500 people were on strike at the Warsaw foundry. The director said the stoppage was confined to two departments and Solidarity leader Seweryn Jaworski, a worker there, was removed from the premises.

Solidarity was established in 1980 in a historic pact with the government. On Dec. 13, 1981, Polish leader Wojciech Jaruzelski declared martial law, and Solidarity was banned. Martial law was lifted in 1983.

Solidarity leader Lech Walesa was not in the shipyard. On Sunday, he told 3,000 cheering supporters he would recommend a strike unless the government promised to talk with striking coal miners.

The government failed to respond.