Few of the 2,000 delegates taking part in the special Communist Party congress that opens here Tuesday need reminding that it was to forestall just such an event that the Soviet Union invaded Czechoslovakia in 1968. Yet, despite the gloomy forecasts of some Western analysts, history does not appear to be repeating itself in Poland.

Despite the recent surge of labor unrest, few Poles doubt that the congress -- which once seemed such a distant prospect -- will take place. Any lingering uncertainty was dispelled by the recent visit here of Soviet Foreign Minister Andrei Gromyko. His talks with Polish leaders ended with a joint communique pledging Polan's "eternal" allegiance to the Soviet Bloc.

The Kremlin seems no closer to accepting the unprecedented changes that have taken place in Poland in the last year. On the other hand, there is no evidence it is prepared to suppress the liberalization movement by force.

The result is procrastination, with the Kremlin putting enormous pressure on the Polish party to stem the tide of change. Few Details leaked out about Gromyko's discussions, but the nature of Soviet concern is evident. It is believed likely that Gromyko urged greater conrols over Solidarity, the independent trade union federation, and the mass media; a crackdown on dissidents and, a most crucial point, halting purges of Communists who are trusted by Moscow.

The Kremlin's past dealings with Eastern Europe illustrate the paramount importance it attaches to having its "own" men in key posts in the capitals of its allies. It is this control of the power apparatus that Moscow fears could be jeopardized by the Polish party congress.

The congress is to elect a new leadership. Moscow can take comfort from the fact that many present members of the Polish Poliburo will probably be reelected, but sweeping changes lower down are likely. Soviet officials appear most worried about proposed party statutory changes under which the rank-and-file would control the leadership instead of being controlled by it.

An account of how the Kremlin views its allies is provided by a former high Czechoslovak official, Zdenek Mlynar, in his recent book "Night Frost in Prague."

It tells of the secret talks of Moscow in August 1968, shortly after the invasion of Czechoslovakia, between the Soviet Politburo and the reformist Czechoslovak leadership under Alexander Dubcek.

In these talks, according to Mlynar's account, Soviet leader Leonid Brezhnev tried to justify the invasion. He said the Soviet Union had suffered enormous material and human losses during World War II. Through those sacrifices, the boundaries of socialism had been expanded to include Eastern Europe, Brezhnev reportedly said, and the results of World War II would be defended even at the risk of a new car.

Another point made by Brezhnev was that, to control Eastern Europe, the Kremlin needed to be able to trust the local Communist leaders to act "in the common interest of socialism."

Recent Soviet pronouncements suggest that the Kremlin has grave doubts on both these scores as far as Poland is concerned.

But the cost of invading Poland would be much higher than in Czechoslovakia. Not only has the world changed since 1968, with the Soviets now having a much greater interest in detente, but the two countries are very different. Unlike the Czechoslovaks, the Poles, it is expected, would fight.

A series of insurrections against foreign (usually Russian) rule has conditioned the Poles to fight, whatever the odds.

If an invasion is ruled out, the next most obvious alternative available to Moscow for retaining control over Poland is economic.

One effect of the Polish crisis has been to increase the country's dependence on the Soviet Union for energy and raw materials. Drained of hard currency reserves, Poland now receives virtually all its imported oil and natural gas from Moscow. Its desperate financial position means that even if it wanted to, it would find it impossible in practice to cut this link.

At the recent meeting of the Soviet Bloc trading organization Comecon in Sofia, Bulgaria, Polish leaders urged more -- not less -- economic integration of the Soviet Union and its allies.

Economic integration is a much more sophisticated method of ensuring Soviet domination than military force, and it is probably equally effective. But this alterantive, too, is very expensive.

According to recent Western studies, the Soviet Union subsized Eastern Europe to the tune of $6 billion in 1978 through the sale of cheap oil and by providing markets for goods of inferiro quality. Last year, the subsidy to Poland alone is thought to have reached $3.8 billion.

This contrasts with the early postwar years, when the Soviet Union was able to profit considerably from its relatively well-developed East European satellites. Now, for political reasons, the Kremlin must subsidize the Poles and other East Europeans to maintain a standard of living that, however modest, is still superior to that enjoyed by Soviets.