A one-hour strike planned for Friday by Poland's independent trade unions could mark the start of a crucial new phase in the Soviet Bloc's most serious political crisis for a decade.

Union leaders have described the action as a token protest against delays in implementing agreements reached a month ago with striking workers along the Baltic Coast and in the industrial region of Silesia. At the same time, the strike also represents a unique event in Eastern Europe's postwar history.

Never before have workers in a communist country been asked to stage an organized protest against the government by an independent labor organization. The strike, which will begin at noon in selected plants, will inevitably be taken as a measure of the strength of the new union federation, Solidarnosc (Solidarity).

As union leaders pressed ahead with their plans to stage the strike, many influential Poles privately expressed concern at the apparent lack of strong political leadership in the contry. An important Central Committee meeting will be held on Saturday, a day after the strike, to draft plans for a new party program.

The plenum, which was originally due to have been held last week, should provide the first firm indication of how far the Polish leadership is prepared to proceed along a more pluralistic road to communism. The [WORD ILLEGIBLE] in holding the meeting sparked off speculation that the still powerful hard-line faction within the Central Committee was resisting proposed reforms.

The last month has seen the gradual petering out of labor unrest combined with attempts by the new unions to win formal recognition by individual factory managements and local authorities. Now begins the key period of testing the stability of the new balance of political forces that has emerged within the country.

Also important will be the reaction of the Soviet leadership to the proven ability of the independent unions to exercise control over a large segment of the Polish working population. One of the most important tasks faced by the new Polish leader, Stanislaw Kania, is to convince the Kremlin that there is no feasible way of going back on the agreements negotiated with the workers.

In a television address tonight, an influential commentator, Mieczyslaw Rakowski, who is also a Central Committee secretary, drew attention to the Soviet interest in developments in Poland by remarking: "The world -- and our friends as well -- are looking to see whether Poles can make the country stable."

In the short term at least, most Poles seem to believe that it is up to them to solve their own problems -- and the Kremlin is unlikely to intervene at this stage. This carefree attitude stems partly from the fact that the Polish press has discreetly refrained from analyzing relations with the Soviet Union, but also because of a general feeling that, short of an invasion, there is nothing the Kremlin can do to reverse the course of events. i

Meanwhile both government ministers and Solidarnosc leaders have been blaming each other for the failure of talks aimed at heading off Friday's strike. A statement issued by the union from its headquarters in Gdansk said that, in talks on Wednesday evening, the government side had guarantees on improved access to the mass media.

The lack of reasonably full an objective reporting of union activities in the state-controlled media is one of Solidarnosc's major grievances. The other is alleged delays in implementing a program of promised wage increases that were due to have been announced by Sept. 30.

Workers have learned about the strike call mainly at their factories. Leaflets have also been distributed calling for discipline during the strike, which will begin and end with the sound of factory sirens all over the country.

At a press conference today, the Polish government spokesman, Jozef Barecki, insisted that authorities were doing all they could to implement undertakings made to the workers. But he accused some union leaders of adding unacceptable new financial demands to those already agreed upon.

"It's not a question of good will on our side, but what's practically feasible. We simply lack the means for implementing demands that go beyond the agreements," he said in a reference to Poland's economic plight.

Government officials say that the economy has been severely disrupted as a result of production losses during the strike and a sharp fall in productivity since in many factories, much time is devoted to political discussions rather than work.

The supply of coal, Poland's chief export, is well below demand and foreign ships waiting to load in the northern Baltic ports are facing lengthy delays. The drop in production has been attributed to the abandoning of an unpopular shift system in Silesian mines designed to ensure continuous work in the shafts.

At a press conference, Heavy Industry Minister Andrzej Zedynak estimated that production losses in heavy machinery as a result of the one-hour strike would amount to 102 million zlotys ($3.3 million). One-third of this figure represents lost exports.

Union leaders, however, claim their aim is not to disrupt production and economic losses will be minimal. Many workers manning equipment that needs to be kept running will participate only symbolically in the strike by wearing armbands in the Polish national colors, red and white.

Barecki said the strike would do great "psychological damage" since the government honestly felt it was doing its best under the circumstances. He said talks on pay rises had been held with all groups of workers, but agreed that in some cases they had not yet reached a conclusion -- despite the Sept. 30 deadline set by the agreement.