Amid slippage in party membership, slackening popular support of work stoppages, and intensified official criticism of the independent Solidarity trade union, Communist authorities moved a step closer to an outright ban on strikes today.

The Communist Party leader, Gen. Wojciech Jaruzelski, said the ruling Politburo had decided to instruct the government to introduce legislation in parliament banning strikes. The announcement came at a meeting of the party's Central Committee, called to discuss Poland's economic problems and plans for reform.

Jaruzelski's remarks on antistrike legislation, conveyed to foreign correspondents here by a spokesman for the government's information agency, were still unreported by Poland's domestic news media several hours later. There was no official explanation for the delay.

The Polish parliament passed an appeal for an end to strikes at the beginning of this month, but it did not have the force of law. Since then, industrial unrest in major factories has largely tailed off, but other groups such as farmers and students have started protests.

The student strike today received the backing of firemen trainees in Warsaw who occupied their college in defiance of repeated ultimatums by the Interior Ministry. Workers from nearby factories were summoned to guard the building to protect the firemen.

Communist Party leaders have warned that, unless parliament's appeal is respected, the government will resort to "emergency measures" to end labor protests. But the exact nature of these proposed measures has never been disclosed, and the difficulties of enforcing any legal ban mean that it could face opposition in parliament.

The legislature is to meet again next week, but there was no clear indication when the government would introduce the legislation.

The Politburo report to the Central Committee today, read by the party secretary in charge of the economy, Marian Wozniak, said national income would fall 15 percent this year, down to the level of 1974. The report accused extremist forces within Solidarity of blocking all the government's attempts to overcome the problems.

"Strike terror weakens the state and systematically destroys the nation," Wozniak said. "For over a year there has not been a complete day of social peace in Poland, a day without either a strike or the threat of a strike."

Jaruzelski, who is also prime minister, was quoted as saying that the idea of a front of national agreement could be realized only in conditions of order and peace.

Both government and union leaders have called for the creation of a national consensus to solve Poland's political and economic problems. Talks between the two sides have been under way for 10 days, but little substantive progress has been reported.

A major difference of approach has become apparent. The Communist authorities are anxious to secure Solidarity's participation in a loosely defined coalition that would shoulder responsibility for tackling the crisis. Union officials, however, want to solve specific problems first and talk about the principles of power-sharing later.

So far, negotiations have centered on formation of a consultative council on the economy. Talks on Solidarity's demands for greater access to the mass media have been delayed by the government, apparently for tactical reasons.

Party strategists may be hoping that time is in their favor. In an interview this week, Stefan Olszowski, the propaganda chief, said polls conducted by state television showed a continuous drop in public support for strikes.

The polls reportedly showed that while 90 percent of Poles supported strikes in August 1980 when Solidarity was formed, a one-hour nationwide warning strike last month won the backing of only 46 percent of the population.

The trend is supported by Solidarity's own research. A poll published by the union's weekly newspaper said 34 percent of Solidarity members believed that most or all strikes are avoidable.

Perhaps even more significant, one out of every four union members supported an earlier call by the Communist Party Central Committee for a ban on strikes. Sixty-five percent opposed any strike ban, but only 5 percent were prepared to use a general strike to oppose a ban.

The statistics reveal a much greater division of opinion than a year ago. Yet, the Communist Party remains deeply unpopular and has failed to increase appreciably its public support.

Meanwhile, it was disclosed at the Central Committee meeting that 244,000 party members had recently resigned and 180,000 more had been expelled for wrongdoing. According to most estimates, the number of party members in Poland is well below 2.5 million, compared with more than 3 million a year ago.