Poland's Communist Party leaders today issued a toughly worded resolution threatening underground activists of the suspended independent Solidarity trade union with severe punishment and pledging to maintain strict controls to prevent a resurgence of social unrest.

The resolution, issued following a two-day meeting of the party's policy-making Central Committee, reflected official concern at continuing protests against martial law. The statement accused the United States of instigating what was described as "an anti-Polish campaign" and attempts at "economic blackmail."

In a modest shakeup in the party leadership, a fourth general was elected as an alternate member to the ruling Politburo. He is Interior Minister Czeslaw Kiszczak, who has been closely associated with the party leader and martial-law chief, Gen. Wojciech Jaruzelski.

The party's economic expert, Marian Wozniak, also was elected an alternate member of the Politburo, which has 14 voting and five alternate members.

Meanwhile two members--Marian Arendt and Jan Malanowski--were dropped from the 198-member Central Committee, apparently because of their Solidarity sympathies and reservations about martial law.

The Central Committee session coincided with a meeting of Poland's Roman Catholic bishops. No formal statement has been released by the bishops but sources at the meeting said that debate has been lively with some participants expressing concern at what they saw as a tougher line being adopted by the government against Solidarity.

One participant said that, at the government's request, a joint church-state meeting planned for Saturday had been postponed. The government apparently wanted more time to consider the results of the bishops' meeting.

Poland's national assembly, the Sejm, has also been meeting at the end of a week dominated by a resumption in political activity. The session was devoted to a discussion of plans for economic reform.

Gustav Holoubek, a prominent actor, resigned as a Sejm deputy, saying he could no longer represent in the Sejm the interests of cultural workers when so many of them were interned and jailed under martial-law decrees approved by the national assembly, Reuter reported.

The Central Committee resolution accused "enemies of socialism supported and inspired by centers of imperialist subversion" of "poisoning the nation's consciousness with slogans of hatred." The protests, it said, had been aimed at exploiting "the credulity of youth" and at "introducing confusion to various social groups."

Scattered demonstrations against martial law have been reported in recent weeks from cities including Gdansk, Poznan, Wroclaw, and Lublin. Warsaw remains calm but underground Solidarity leaflets continue to circulate.

The Central Committee resolution said that the organizers and participants in such protests would "be punished with the utmost severity of the law." Trials of strike organizers have been continuing in several towns with sentences averaging between four and six years.

The Central Committee, meeting for the first time since the Dec. 13 military crackdown, formally endorsed the martial-law decrees. The decision to impose martial law, the resolution said, had been taken "to prevent national catastrophe" after all other means had failed.

The resolution also called for a purge from the party of all members who failed to meet "high moral requirements." It described factional activity as "inadmissible" and urged a halt to the "activity of any movements, structures, forums and seminars that go beyond the party statute."

The best organized of the informal Communist Party discussion groups that sprang up around the country over the past few months are the so-called rzeczywiscosc (reality) clubs, which reflect hard-line opinion. Their main patron has been the party's ideological chief, Stefan Olszowski.