Poland's independent Solidarity trade union's first congress issued a bold expression of support for free trade union activists throughout the Soviet Bloc today. The congress also challenged the Polish government to hold a referendum on the critical issue of worker self-management.

The two resolutions were passed by overwhelming majorities of the 892 delegates as the congress moved into an unscheduled fourth day. Both are likely to seriously embarrass Poland's communist leaders, who are anxious to play down Solidarity's appeal in the rest of the Soviet Bloc and to restrict the scope of internal economic reforms.

The issue of workers' self-management lies at the heart of the changes in Poland during the last year. The demand for a referendum on the government's plans could develop into another major struggle between the two sides.

Solidarity has put forth a proposal for workers' self-management which goes much further than the government's does in introducing market mechanisms into the economy. It also would give workers the right to elect their own directors. Implementation of the Solidarity proposal could effectively remove ultimate control of the economy from the state.

In its other resolution, the Solidarity congress expressed support for fellow East European workers "who have resolved to enter the difficult road of struggle for free trade unions." It added that it hoped to organize a meeting of all free trade unionists active in the region.

The message was addressed to the workers of the six other Soviet Bloc countries -- the Soviet Union, Czechoslovakia, East Germany, Romania, Hungary and Bulgaria -- plus Albania, which pursues an independent line but ruthlessly represses all forms of dissent.

The resolution said: "We assure you that, despite the lies perpetrated in your countries about us, we are an authentic union representing the workers and born out of a workers' strike. Our aim is to struggle for better living standards for all working people."

There have been sporadic attempts to set up free trade unions in Eastern Europe but, apart from Poland, none has yet met with any success. Elsewhere, the "free trade unionists" have been severely harassed by security forces and law courts.

The resolution challenging the government to hold a referendum on workers' self-management results from Solidarity's criticism of an officially inspired draft law scheduled to be debated by parliament later this month as inadequate. However, Communist Party leaders insist that the state must retain ultimate responsibility for directing the economy and appointing managers.

The resolution passed by the Solidarity congress today called on parliament to conduct a referendum allowing Poles to choose between the two rival schemes. If this suggestion is not accepted, it added, the union would conduct its own referendum and boycott the self-management bodies set up under the new law.

With 9.5 million members, Solidarity commands the loyalty of between 70 and 80 percent of the country's work force. Under its auspices, informal workers' councils have already established themselves in many Polish factories.

Commenting on the resolution, union official Karol Modzelewski predicted that the parliament -- dominated by the Communist Party -- would reject the idea of a referendum as "they are not suicidal." He added: "That means we shall go ahead with our own plans."

Solidarity has already organized one referendum, on a smaller scale, in the giant Katowice steelworks in the southern industrial region of Silesia. The main question was whether to remove the plant's director who had earlier ordered the closure of a union newspaper for publishing anti-Soviet cartoons.

Union officials said most of the 19,000 workers at the steel mill had voted in the referendum--and that the result would be announced later this week.

The party has described its commitment to economic reform as far-reaching and irreversible, but this has been challenged by Solidarity. Union officials described the government draft as suggesting that "the reform is intended to change everything, but in such a way as to change nothing."

A resolution passed by the Communist Party's Central Committee last week said the official plans were designed to turn "independent, self-managed, and self-financing enterprises" into the basic economic unit.

Under the old system of central planning, individual factories were required to implement hundreds of frequently impractical directives drawn up by a labyrinthine bureaucracy in Warsaw.

This system has now fallen apart, but the party is unwilling to loosen its grip over the economy entirely. In a speech to the Central Committee, party leader Stanislaw Kania said the state would never give up its role of conducting personnel policy in the national economy.