Poland's leader, Gen. Wojciech Jaruzelski, briefed senior political and military officials today on plans that he is expected to announce Wednesday for relaxation of martial law. He will address the National Assembly following shifts in the Communist Party hierarchy thought to have strengthened the general's position.

Polish Foreign Minister Jozef Czyrek held a similar briefing for Pope John Paul II at the papal summer residence outside Rome today. The one-hour meeting reflected a recognition by the Polish government that it needs the support of the Roman Catholic Church to maintain social peace.

Speculation has been mounting here for weeks that Jaruzelski will announce significant concessions, including the release of hundreds of political prisoners. The speech, coming a day before Poland's national day on Thursday, is being billed by officials as containing the blueprint for development over the next six months.

Jaruzelski met today with members of the military Council for National Salvation, the body set up to administer martial law, and leaders of the political parties represented in the assembly. The meetings followed a plenary session of the Communist Party's Central Committee last week.

At the Central Committee meeting, Jaruzelski eased out a potential rival, Stefan Olszowski, from the key post of party secretary for propaganda. By doing so, he appeared to strengthen his personal position and increase his room for political maneuver. The general is not only commander in chief and defense minister but also premier and party first secretary.

Differences of opinion within the party hierarchy were one of the main factors contributing to the mood of political stalemate that has gripped Poland over the past few months. Conservatives in the party apparatus, represented by Olszowski, were believed to have opposed what they saw as a "soft" approach toward the suspended Solidarity trade union.

Official sources said that Olszowski's removal might allow Jaruzelski to pursue more conciliatory policies, particularly in the field of mass media. It could also have symbolic significance in helping to persuade underground Solidarity leaders, as well as the church, of the government's willingness to look for a negotiated solution to political and economic problems.

A more cynical interpretation is that Jaruzelski was primarily concerned with defusing a threat from an ambitious politician with a strong following in the bureaucratic apparatus. According to this view, the policy differences between the two men are not as great as is sometimes supposed.

Western diplomats here note that Olszowski is far from being in disgrace. He has retained his membership in the ruling Politburo and is slated for a senior post in the government, possibly that of foreign minister.

Since imposing martial law last December to suppress Solidarity, Jaruzelski's tactic has been to bolster his own centrist following in the Central Committee by slicing away the two extremes. "Liberals" and "hard-liners" have been sacrificed in almost equal proportions in a series of small, but cumulatively significant, personnel changes.

Olszowski's ouster as propaganda chief was preceded by the removal of the hard-line Communist Party bosses of Warsaw and Katowice, Stanislaw Kociolek--since named ambassador to the Soviet Union--and Andrzej Zabinski. The liberals were depleted by the dismissals of Tadeusz Fiszbach and Edward Szczypczak as party secretaries in Gdansk and Poznan and, last week, Hieronynym Kubiak as party secretary for education and culture.

The prospect of relaxations in martial law have encouraged underground Solidarity activists to call for a moratorium on strikes and demonstrations. Earlier this month, leaders of the Solidarity underground said in a statement that the possibility of agreement with the authorities still existed.

The statement, which was published in clandestine Solidarity bulletins, was notably more restrained than previous appeals. It called for "the cessation of mutual accusations" and implied a readiness by Solidarity to forego political activity.

"We don't want to be either a government or a political party," the statement said. "We want to be an independent and self-governed union movement. The next chapter of our country's history should be written afresh." It was signed by three members of Solidarity's provisional coordinating commission: Zbigniew Bujak, Wladyslaw Frasyniuk and Bogdan Lis.