For more than 30 years, the term "salami tactics" has been used to describe communist governments slicing away at their opponents. But not reformers in Poland are using the old salami tactics to construct a radically new kind of communist society.

The phrase was coined by the Hungarian Stalinist leader Matyos Rakosi to describe the way he gradually isolated opposition political parties which would not accept communist domination of Hungary in the late 1940s.

It was used again in 1968 to describe the "normalization" process in Czechoslovakia following the 1968 Soviet invasion: Reforms introduced by Alexander Dubcek were sliced away gradually until there was no salami left at all.

In Poland, the same phenomenon is taking place -- only in reverse. Week by week, month by month, one slice of reform is being added to another. Individually, the changes are sometimes difficult to perceive, but cumulatively they amount to the creation of a system of government unlike any other in Eastern Europe.

Today's May Day celebration in Warsaw provided a good illustration of the process. The traditional parade through the center of the city was ignored by the independent Solidarity trade union. Instead of standing on a reviewing stand as is customary, Communist Party leader Stanislaw Kania and his top lieutenants made a gesture to democracy by mingling with the crowds.

Nevertheless, the fact that the communist authorities managed to attract as many people onto the streets as they did -- the march took two hours to pass a single point -- was a considerable achievement. It strengthened the impression of gradual, and controlled, change that Kania is seeking to project.

Judging by his actions so far, Kania's hope is that by moving slowly in a reformist direction he can satisfy Polish people without alarming the Soviets unduly. His dilemna is that neither he nor anybody else here can judge exactly which point along the salami represents the outer boundary of Soviet tolerance.

After so many twists and turns following the initial explosion of labor unrest last summer, it is difficult to predict the future course of events in Poland. But there is a general feeling here that the next 10 weeks could determine whether Poland will be allowed to solve its problems by itself or whether the Soviet Union will again use military force to crush liberalization movement in Eastern Europe.

The reason for the cutoff date is that the firm decision has been reached to hold a special congress of the Polish Communist Party July 14-18. By electing a new leadership and drafting a new program, the congress is, in effect, charting the party's course for the next five years.

The Soviets timed their invasion of Czechosovakia for Aug. 21, 1968, to; forestall just such an event. An extraordinary Czechoslovak party congress had been called for Sept. 14. Had it gone ahead, and endorsed Dubcek's policies, the reform movement in Czechosolovakia would have been that much more difficult to reverse.

There are plenty of differences between the Czechoslovak and Polish cases. The costs to the Soviets of invading Poland -- in human, political, and economic terms -- are much higher than they were in Czechoslovakia. This itself makes outside intervention here less likely.

The run-up to the congress is, nevertheless, a delicate period. As a Polish official remarked, "We feel that if we get through the congress, things will gradually settle down. But we know that we can run into big problems between now and then."

Polish officials confirm privately that the Kremlin's main preoccupation now is not Solidarity, but the growing reformist trends within the Communist Party itself. It was this concern, that provoked a visit here last week by Moscow's chief ideologist, Mikhail Suslov, and an attack on "revisionism" in the Polish party by the Soviet news agency, Tass, two days later.

The latest concession to the reformers is the election to the ruling Politburo of two worker-members of the Central Committee. At the same time, Jozef Pinkowski, who resigned as prime minister in February, has now been dropped from the Politburo as well.

The two workers were elected in a secret ballot during the closing stages of the Central Committee plenum. Later, the offical news agnecy, PAP, took the unprecedented step of publishing the results of the vote: 111 out of 140 for General Gabrys, a 48-year-old miner from Silesia, and 110 for Zygmunt Wronski, 49-year-old machine operator from the Ursus tractor factory near Warsaw.

Unlike the vast majority of Polish workers, neither Wronski nor Gabrys belongs to Solidarity. They are veteran communists and secretaries of their local party organizations. Their election to the Politburo, which now has 11 members, should have the effect of strengthening Kania's personal grip on the leadership. It is likely to prove much more difficult for the conservative faction in the Politburo to challenge his authority.

In a closing speech at the meeting, Kania described the increased role of workers in the party as "an important prerequisite for its consolidation."

The Central Committee stopped short of removing any of the principal hard-liners led by the propoganda chief, Stefan Olszowski. Officials explained that, with the party congress so close, it was considered "not the right moment," for any major reshuffle of the leadership.

Even some dissidents find the current reformist drive within the party alarming. A member of the Committee for Social Self-Defense, known as KOR, remarked recently: "We would prefer the party to be unreformed, to be an orthodox figleaf for all the liberalization taking place elsewhere. That way, it could still act as a guarantee to the Russians."

It was, however, unrealistic to expect that a reform movement that shook up every other area of Polish society could leave the Communist Party untouched. Sooner or later, ordinary party members were bound to be affected by the national mood -- particularly since well over one-third of them also belong to Solidarity