Riot police broke up a gathering of thousands of Poles on the anniversary of the 1956 Poznan worker riots today, charging into a crowd that fled chanting, "Gestapo, Gestapo."

The crowd, numbering close to 5,000 at its peak, had converged in the center of Poznan to lay wreaths at a monument in memory of workers killed on June 28, 1956 in a clash with police.

The memorial was dedicated a year ago after the independent trade union Solidarity convinced authorities it should be erected. Its inscription reads, "From this place, for the first time, they claimed the people's right to mass dignity."

An official ceremony to mark the anniversary was held yesterday, but Solidarity told its supporters to boycott it, urging instead that Poles mark the occasion with individual visits to the memorial after work today.

Heeding that call, employes of the Cegielski engineering plant--whose workers in 1956 mounted the demonstrations that led to the riots--went to the monument today.

While streetcars rattled empty down the avenue in front of the factory, the workers walked in small groups through cold, driving rain. By midafternoon they and workers from other factories had gathered in front of the monument. Most moved briskly under the watch of militiamen who checked documents.

The atmosphere was one of quiet defiance without outward signs of agitation. As the crowd grew, militia vans staged a show of strength on the main street. From a loudspeaker, the militia ordered the group to leave to avoid "more direct police action." These instructions were met with jeers, hoots and whistles.

The Zomo, Poland's motorized security police, moved in and confronted the crowd that had dwindled to several thousand. They pushed bystanders out of the way and chased those who remained down wide avenues. Although the militia had threatened to use tear gas and water cannon, they dispersed the crowd without using it.

This year's confrontation contrasted with the celebration last year when tens of thousands of Poles--Solidarity supporters and party officials alike--stood shoulder-to-shoulder to hear a speech by Solidarity leader Lech Walesa, who has been detained since December.

Today's incidents underscored the deepening divisions in this country, which has been under martial law since Dec. 13.

Two International Red Cross officials and a physician said today that they visited Walesa Saturday, for the second time since his detention, Associated Press reported. They said they met with him 3 1/2 hours at a government resort area near the Polish-Soviet border but they refused to comment on his health or the conditions of his internment--a condition reportedly set by Polish authorities.

Those who gathered showed contempt for the security forces although they did not seek out a confrontation. Recent bulletins from the Solidarity underground in Poznan, the main industrial city of east central Poland, had urged that people gathering at the monument "not allow themselves to be provoked."

Remarking on the crowd's attitude, a Solidarity activist who works at the Cegielski plant said, "They see the potential for a situation like 1956 and they are against it."

A confrontation between police and demonstrators also was reported in Wroclaw, a one-time Solidarity stronghold 100 miles south of here.

In a related development, Poland's Roman Catholic bishops, in a statement after a conference in Koszalin, said that Pope John Paul II wants to return to Poland and "must be given a dignified welcome in the conditions of peace and solemnity."

The bishops said it was the "obligation of those in power" to open a dialogue with social groups. "We shall not overcome this crisis by the abuse of force and the use of violence," the bishops said.