Polish leader Wojciech Jaruzelski, under pressure from a variety of groups within the ruling communist party, has postponed reforms of the economy and toughened repression of his opposition in an effort to maintain control over a crucial party congress in June, diplomats and party sources here say.

At stake in the congress of the party, formally called the Polish United Workers' Party, is the future course of Jaruzelski's drive to decentralize and liberalize economic management, party officials say. Jaruzelski, they say, also hopes to reshape the role of communist leadership in a society that repeatedly has rebelled against its totalitarian style.

Nevertheless, diplomats and party sources point to a number of signs that Jaruzelski faces strong resistance from party groups, ranging from industrial workers to entrenched bureaucrats and ideological dogmatists, who have questioned both the direction of government policies and Jaruzelski's leadership of Polish communists toward a lower and less commanding profile.

"We are fighting on one side against bureaucracy and a tendency toward overcentralization of power, and on the other side against . . . populism among the people," a supporter of Jaruzelski said. "You can clearly see resentment in many workers. Jaruzelski cannot afford to take too many big steps -- and he must take some that he doesn't like."

The struggle over the congress began in earnest last month with a meeting of the party Central Committee. It follows the staging of elections for the legislature and reorganization of the government last year and is seen by officials close to Jaruzelski as a decisive phase in his plans for consolidating and institutionalizing the political leadership he has built in the four years since his suppression of the independent Solidarity union.

"Jaruzelski and the state leadership have had two big battles to win in order to achieve stability," said a party activist involved in preparations for the congress. "The first was the elections to the parliament, and the second is the party congress. The challenge is to win the possibility to build socialism in a way that is understandable and acceptable to the Polish people."

After focusing his policies in the years after Solidarity on quelling active internal resistance and seeking some public acceptance for his rule, Jaruzelski recently has shifted his focus back to party affairs that he sometimes has neglected. He has resigned his job as premier and taken charge of intraparty relations from his principal post as first secretary.

Among the signs of trouble cited by Jaruzelski's supporters are the recent downgrading of an amnesty for political prisoners, first suggested by Jaruzelski himself during a visit to the United Nations, to a "humanitarian initiative," excluding most well-known prisoners. The reversal indicated that Jaruzelski's original plan had been blocked by high-level resistance, several observers said.

In addition, several sources said the government's failure to announce major new measures in the three-year-old effort at economic reform was forced by the need to avoid new controversy before the congress.

"Jaruzelski won't try anything new in economic reform," one western diplomat predicted. "He will try to encourage people to implement the measures that have already been taken. But they won't try to push it, because they can't."

Although some observers say they believe Jaruzelski's own position may be threatened by the opposition within the party, most diplomats and party officials say the resistance is divided among groups with different political agendas who lack the cohesion and leadership to threaten the general's hold on power.

Jaruzelski's personal authority at the top of the party has seemed to grow in recent months, with his removal of several personal opponents and hard-line dogmatists. But while "Jaruzelski will survive the congress, he is under terrible pressures," another western diplomat said. "The danger is that policies he doesn't want will be forced down his throat, and those policies will make it impossible for him to stabilize the country."

While Jaruzelski may be capable of forcing his program on reluctant party factions, officials close to him say, he is constrained by the need to avoid the open battles that beset the communists during their last congress in 1981, during the Solidarity era.

"Jaruzelski must not let the hard-line factions close the way for his policies, but he must do it in an atmosphere of order. It must be a quiet congress," one supporter said.

"To open some big competition would undermine all our arguments that there is stabilization in Poland," he added. "It would be an argument against Jaruzelski for [President] Reagan as well as for [Soviet leader Mikhail] Gorbachev. So Jaruzelski must win with arguments, with instruments of power, and with very clever tactical steps."

The tactical maneuvering already has begun. Seeking to head off leadership battles on the local level, party leaders recently changed traditional procedures and postponed the election of second-rank officials until after the congress. Meanwhile, Jaruzelski has moved selectively to clean up potential trouble spots. Four provincial party secretaries were reported replaced within four days recently.

Nevertheless, party supporters say Jaruzelski has only begun the more difficult task of persuading members at all levels to embrace his policies. In recent party-oriented speeches, he has stressed that the first priority of the congress should be endorsing the program of introducing market forces into the economy and mandating further decentralization of management.

However, debates at the recent Central Committee meeting and the official press have hinted at widespread criticism within the party of Jaruzelski's economic measures.

Party officials say many workers oppose the job insecurity and differences in wages that reforms may bring, while the large central administration that has controlled economic activity for decades has a natural interest in preventing the erosion of its power.

A report Jan. 12 in the Warsaw daily Zycie Warszawy conceded that some opinion now favors "suspending the economic reform for three years."

In overcoming this resistance, party supporters say, Jaruzelski faces the related problem of consolidating a political role for communists that restores their leadership while moderating the dictatorial control over administration and jobs they wielded until the upheavals of the Solidarity era.

Jaruzelski's view, according to a senior party spokesman who asked not to be named, is that "the party must retain some distance from the administration. It must become more of a watchdog than a center of direct control. We cannot return the party to its 'strong' position before 1980 -- because it was exactly that 'strength' that led to a crisis."

Many party veterans, however, have interpreted Jaruzelski's proclaimed "normalization" of the political situation as a signal that the party's profile and prerogatives should be restored, the official said. There has been criticism in party ranks that Jaruzelski and his chief aides have acted as an "administrative clique" based outside the party that has ignored its interests.

Even if Jaruzelski succeeds in overcoming such conservative interests, critics from Poland's still formidable opposition argue that his leadership will not be capable of the economic and political reforms necessary for a genuine stabilization of the country.

"Jaruzelski has already moved toward the position of the hard-liners to such a degreee that the difference, for society, is not that significant," said sociologist Jadwiga Staniszkis. "The result of winning in the party is his own increasing isolation."