Poland's military authorities today stepped up security measures in Warsaw and other cities on the eve of an important session of parliament, which is expected to dissolve the suspended Solidarity trade union.

Riot police trained in dispersing demonstrators and breaking strikes moved back into several hotels in Warsaw in apparent anticipation of trouble. Underground Solidarity leaders, however, still seemed undecided on how to react to the imminent delegalization of their union.

The government press spokesman, Jerzy Urban, told a press conference that even if parliament amended a draft law setting stringent conditions for trade-union activity, that would not affect a clause withdrawing the registration of existing unions, including Solidarity.

Urban said that according to a recent opinion poll conducted by the authorities, 34 percent of those questioned favored setting up new unions against 39 percent who wanted to maintain the old ones.

In a speech to Communist Party members near the central city of Lodz, Deputy Premier Mieczyslaw Rakowski acknowledged that Solidarity's delegalization could provoke strong reactions from some people. But he said the measure was indispensable since Solidarity members had failed to repudiate their "extremist" leaders.

"I think the best solution is to treat the Solidarity era as a closed chapter in the history of the trade-union movement," he said. "Closing the chapter does not mean condemning everything that happened then. It means opening a new chapter and the creation of opportunities for getting out of the chaos."

Solidarity sources said the remnants of the union leadership who escaped arrest when martial law was declared in December were divided over how to react to the government move. Some favored a total boycott of the new unions while others advocated attempting to dominate them.

The draft law stipulates that unions will be re-established from the end of this year at the factory level only, with just one union allowed per factory.

Leaflets circulating in Warsaw called upon Solidarity supporters to remain calm over the weekend and await further instructions. "Let us and not the government choose the date and place for protest against the dissolution of Solidarity," the leaflets said. The authenticity of the leaflets could not, however, be confirmed.

The formulation of a response by Solidarity to the new legislation seems to have been complicated by the arrest earlier this week of Wladyslaw Frasyniuk, one of the union's top four underground leaders. Frasyniuk was arrested on Tuesday afternoon in his hometown of Wroclaw in southwestern Poland.

Newspaper accounts said he possessed a false identity card, had grown a beard and dyed his hair. "You win this round," he was quoted as telling security police when he was detained in the stairwell of a local apartment building. He was said to have been on his way to meet with fellow underground Solidarity activists.

Solidarity sources said that a roundup of other activists appeared to be in progress and that several people associated with the Warsaw underground newspaper Tygodnik Mazowsze had been detained by police.

A former adviser to the union said that Frasyniuk's arrest could result in the adoption of more radical policies by the underground in Wroclaw, which is one of the strongholds of support for Solidarity and resistance to martial law. Frasyniuk's likely successor as head of the union's Wroclaw branch, Konrad Morawiecki, was reported to favor "much more extreme" tactics.

A senior adviser to the Roman Catholic Church, meanwhile, revealed that the primate of Poland, Archbishop Jozef Glemp, had turned down last Friday and again Tuesday requests for meetings with the country's military leader, Gen. Wojciech Jaruzelski, in order to show his disapproval of the planned legislation. He was reported as telling a government emissary that he saw no point in such a meeting until the government responded to a detailed memorandum outlining the church's views on resolving the political crisis.

The church adviser said that, during previous meetings, Jaruzelski had assured Glemp that Solidarity would eventually be allowed to resume its activities. It was not known if that remained Jaruzelski's view.