Thousands of Poles shouting "Down with communism" and demanding revitalization of the banned Solidarity union rallied Friday in several cities on the 70th anniversary of Poland's independence as a modern state, activist sources said.

Police did not hinder the demonstrations which came as Communist authorities, who for 40 years virtually ignored the anniversary of Polish independence, marked the occasion with a memorial service, a concert and other events.In Warsaw, some 15,000 people, many carrying torches, gathered in Old Town after a mass at St. John's Cathedral at which participants prayed, "May our Motherland achieve a true freedom."

Unhampered by police, the growing crowd slowly marched a mile and massed at the Tomb of the Unknown Soldier, shouting "Down with communism," "Independence" and "Solidarity," and waving scores of Solidarity banners.

Police even directed traffic around the crowd, which included more than 2,000 students who had marched earlier from Warsaw University and passed near the Opera House where Polish leader Wojciech Jaruzelski and other dignitaries attended a gala concert.

In the southwestern city of Wroclaw, 3,500 to 4,000 people rallied at a transport depot where the local Solidarity chapter was founded chanting, "We demand the re-legalization of Solidarity."

The crowd swelled from a few hundred in downtown to 10,000 at some points before reaching the depot, activist sources in Wroclaw said by telephone.

The marchers also yelled, "Hands off the Lenin shipyard" and "Down with Rakowski" to protest Prime Minister Mieczyslaw Rakowski's decision Oct. 29 to close the shipyard cradle of Solidarity, which was born in 1980 and outlawed in 1982.

In the medieval capital of Krakow, some 2,000 people chanting pro-Solidarity slogans gathered before the cathedral, again without a sign of police.

Police, normally present in force for independent demonstrations, maintained a low profile at rallies apparently on orders not to mar the official commemoration of the founding of the modern Polish state.