Poland's Communist Party has postponed a meeting of its policy-making Central Committee because of continuing internal party differences, according to party sources, who indicated that a fresh hard-line challenge to the country's leadership was forming.

A harsh attack by a leading Soviet publication--rebutted by supporters of Poland's leadership this week--and pressures from party figures advocating a tougher response to efforts to revive the banned labor union Solidarity have challenged the policies of the Polish leader, Gen. Wojciech Jaruzelski.

Signs suggest old antagonisms are reemerging and a new round of ideological struggle is under way, possibly throwing Jaruzelski on the defensive, although the signals are still tentative and piecemeal.

The developments come amid an ideological and political tug of war here as Poland braces itself for the second visit of Polish-born Pope John Paul II, scheduled for next month. A range of groups, including the Roman Catholic Church, opposition elements and Communist Party hard-liners, are feverishly pressing Jaruzelski to alter his policies.

The papal visit--if it happens at all--could, in the view of observers here, usher in a new period of less-repressive rule in Poland or trigger a post-visit crackdown.

The church, a powerful force in this heavily Catholic state, needs a moral victory--beyond having won a second papal visit to Poland in four years--to balance the potential political gain for the Warsaw government of a visit by such a world leader. Hitting hard on civil rights concerns, church officials have repeatedly appealed for an amnesty for political prisoners, for the lifting of the remaining martial law restrictions and for the reinstatement of union activists fired from their jobs.

Adding to this list a call for trade union pluralism, former Solidarity chairman Lech Walesa and other union activists have stepped up their agitation for a more democratic labor movement. Encouraging this opposition drive has been the lack of popular support for the official trade unions and a surprisingly strong turnout on May 1 for pro-Solidarity demonstrations in the face of massive police intimidation.

Jaruzelski, meanwhile, is trying to hold his ground at least until the papal visit, feeling pressure as well from Soviet and other hard-line circles not to make concessions.

"All sides know that the issue is who gains what before the pope arrives," said a Pole who has active contacts to senior state, church and opposition members. "The question is, who will eventually bow down?"

Such tensions could be contributing to a seeming erosion in the control that Jaruzelski has exercised over his party up to now.

The exceptional alliance forged with the introduction of martial law 17 months ago--among the party's reform-minded groups, its hard-line factions and national security forces--may be breaking apart.

In the most ominous sign of new hard-line pressure, the Soviet paper New Times last week published an article accusing the Polish weekly Polityka, a flagship of party progressives, of undermining Poland's socialism by encouraging the expression of pluralism. It attacked several leading Polish party theoreticians and journalists.

Also criticized, but not by name, was Mieczyslaw Rakowski, former editor-in-chief of Polityka and now, as deputy prime minister, a key architect of Jaruzelski's limited reforms.

"The number of attacks on those generally associated with the liberal side of the Polish government and party have increased in a whole chain of papers belonging to the hard-line side," observed a Pole who has been a target of the assault. "This is another wave of something we've experienced before."

The party, which senior officials have publicly admitted was near collapse during the time of the Solidarity trade union, lost one-fourth of its members in 1981 and 1982. It has not been able to reach agreement on an ideological program since a national congress nearly two years ago and now reportedly has postponed a Central Committee meeting scheduled for mid-May to discuss ideology.

In an article in tomorrow's edition of Polityka, government spokesman Jerzy Urban, a close friend of Rakowski, acknowledges that party hard-liners--whom he alludes to as "hoorah revolutionaries" and "slogan maniacs"--are contributing to the current rise in Polish political tensions.

Urban claims these hard-liners "lack troops they can summon to battle" but that this does not seem to discourage them.

If the makeshift alliance between party reformers and hard-liners plus security forces is wearing thin, then the progressive elements of Jaruzelski's program--the economic reform, the promise of a constitutional guarantee for private farm ownership, the expressed desire for improved relations with the Catholic Church--could be in danger.

Party bureaucrats have never been enthusiastic about the economic reform, which threatens to diminish their authority, and they resent the substantial shift in power that has taken place under Jaruzelski from the party apparatus to the state administration.

At least some elements of the Soviet leadership may consider it convenient to encourage the infighting in Poland in order to force Jaruzelski to toughen his line.

It is also true, however, that Jaruzelski may find it to his advantage in negotiations with the Catholic Church to appear weakened and under fire from hard-line and Soviet circles. He could then argue that he has no room for granting concessions.

In any case, these political jitters frustrate the launching of any sanctioned initiatives. The first national congress last weekend of the Patriotic Movement for National Rebirth--an organization heralded by authorities as offering the average citizen a voice--failed to produce anything specific that the government could respond to in a compromise gesture toward society. Instead, its resolutions were cautiously watered down and conflicts were muffled.

Pointing up the political shallowness of that congress, a group of nine people, including Walesa and former leaders of unions abolished last October, sent a letter to the Polish parliament that said more about the aspirations and desires of a great segment of the country than did the many documents passed at the congress.

The letter was meant to undercut the charge by authorities that such opposition groups do not want reconciliation, only street protests and destabilization, according to one who was asked to participate in the letter-drafting session.

Noting that "deep changes in the opinions and attitudes of the nation" had occurred during the Solidarity period, the letter said "a new quality was created which must be recognized and considered by those who govern."

Participants in the meeting were jailed and interrogated by police for two days. Urban told reporters this was done "to prevent initiatives that could disrupt public order."

Official warnings to Walesa and other opposition activists have gotten sharper and more insistent in recent days. In private conversation, some officials, who argue that the government has been lenient in not jailing Walesa since his release from internment last November, indicate their patience is waning.

This air of confrontation between the authorities and a large segment of society, and between state and church, provides a climate for provocateurs who want to force a cancellation of the papal visit.

Such a factor may have been behind the attack last week on a Warsaw convent that houses the Roman Catholic primate's aid center for jailed Solidarity activists and their families. The intruders, who beat up several of the aid center's lay volunteers, went out of their way to appear to be plainclothes security agents, possibly hoping to cause a rupture in church-state relations over the incident. Both church and state have drawn a curtain of silence over the matter, after trading strong protests in private.

Meanwhile Reuter reported that Polish authorities have jailed the Rev. Stefan Dzierzek, 68, a Jesuit priest, for two months after he appealed for donations to help those arrested in opposition demonstrations on May 1. Dzierzek, who lives in Kalisz, has delivered many strong sermons condemning military rule, Reuter said.