Polish authorities confirmed today that the slain pro-Solidarity priest, the Rev. Jerzy Popieluszko, was strangled by his kidnapers before being thrown into a reservoir last month and said three secret police officers who confessed to the crime will be formally indicted for the murder.

Today's announcement came almost three weeks after the last extensive details disclosed by officials about the case, which began Oct. 19 with the abduction of the 37-year-old cleric.

The Interior Ministry superior of the three, a colonel, also faces indictment.

The general prosecutor's office is reported still to be searching for possible accomplices, but no major breakthroughs have emerged during the last couple of weeks. The apparent lack of momentum has led some supporters of Polish leader Gen. Wojciech Jaruzelski to fear that time is running out for him to capitalize on the political uproar caused by the attack to root out hard-line opponents in the security services and in the party.

These supporters say this is a critical period for Jaruzelski and his close ally, Gen. Czeslaw Kiszcak, the interior minister, both of whom are champions of centrist, pragmatic policies promoting accommodation with the church and restrained use of force against the opposition.

Given Jaruzelski's reputation as a cautious politician, and his natural reluctance to shake up too much of the security apparatus on which he still must heavily rely, the betting odds here favor only a partial purge of hard-liners.

But Jaruzelski's dilemma, according to supporters and critics alike, is that unless he takes advantage of the provocation posed by the priest's killing to move against his political challengers, his own position in the party and society may be irreparably weakened.

Jaruzelski has taken over direct party control of the security services, curbing the power of Miroslaw Milewski, a hard-line apparatchik.

But Polish officials say the momentum of the investigation has been stymied in part by the refusal of the kidnapers to implicate higher-ups, if there are any. Some government and party members maintain the policemen must have had high-level political backing from somewhere to perpetrate such a drastic act.

Government spokesman Jerzy Urban told reporters today that the investigators have not ruled out the possibility of a broader conspiracy, presumably involving other security agents or hard-line party members who conceived the killing to undermine Jaruzelski. But Urban said last week that such a break in the case may not come until the trial, and no trial date has yet been announced.

As a curious sidelight to the case, Polish authorities announced 11 days ago the arrest of Kazimierz Mijal, a onetime high-ranking communist who sided with the party's Stalinist faction in the 1950s and early 1960s. He defected to Albania in 1966 when his hard-line cause here seemed lost, set up his own Polish Communist Party there and ran a Polish-language section at Radio Tirana. After Albania's break with China, he moved to Peking, then to Brussels and is officially reported to have returned to Poland in the summer of 1983 using false documents.

Urban loosely linked Mijal to the Popieluszko affair inasmuch as the diehard Stalinist was caught delivering around Warsaw -- to embassies and Polish institutions -- leaflets justifying the Popieluszko murder as an outgrowth of the government's tolerant attitude toward the clergy.

Most Poles viewed the news about Mijal as something of a comic interlude in the tragic drama of finding all those responsible for Popieluszko's death.

But the fact that Polish authorities felt compelled to yank him off the streets at this time is widely interpreted as reflecting a general jitteriness in party ranks. Mijal's public reappearance did at least highlight the factionalism that has plagued Poland's Communist Party since its early days.

Jaruzelski's measured, reformist approach is largely in line with that of Polish leaders of the past 30 years, since Wladyslaw Gomulka in 1956 bested a Stalinist faction. Gomulka ushered in policies of limited cooperation with the Roman Catholic Church, the decollectivization of agriculture and halting stabs at economic reform.

Informal but well-defined splits within the Polish party have nonetheless persisted. From outside, the party is often seen as a creature of Soviet masters and bureaucratic opportunists. But inside, party bosses have become preoccupied at times with power struggles pitting patriots against cosmopolites, hard-liners against reformers, and more recently, civilian apparatchiks against military officers promoted to senior positions by Jaruzelski.

Ideologically, the Polish party has been divided between the Stalinists and those who favored variations on flexible "national communism." Even among the Stalinists, there have been rifts between between those who have sought to turn Poland into a pale imitation of the Soviet Union and those who have wanted to use Stalinist methods to create a fiercely independent but uncompromisingly dictatorial Polish government.

Toward the end of his reign, Gomulka again faced a hard-line challenge, this time from a faction led by Mieczyslaw Moczar, the minister of interior. Moczar had built up a power base among wartime partisans, veterans noted for their intolerant, Philistine attitudes. Moczar's militia kicked off a political power struggle by using excessive force to quell a student protest in Warsaw in March 1968.

As the rest of the nation watched dumbfounded, the party and government were plunged into a wave of purges, anti-Semitic slander, a pandering to nationalism, denunciations of supposed revisionists and an onslaught against intellectuals.

Moczar eventually lost, but so did Gomulka who fell in 1970 when worker riots brought a new reformer, Edward Gierek, to power. But the promise of change and progress soured under Gierek, too, and although he banished two hard-line leaders of a group that emerged to challenge him in 1978, he was himself toppled in 1980 by the rise of Soldiarity.

In the tumultuous 16 months that Solidarity survived, the party's hard-line factions were active and evident.

While the imposition of martial law in December 1981 seemed a victory for the hard-liners, their satisfaction was brief. Jaruzelski showed in time that he favored a number of the policies they abhorred: including concessions to the church and approaches to the west. Last summer he granted amnesty to nearly all Poland's political prisoners.

Worse, in the hard-liners' view, Jaruzelski seemed to be succeeding in normalizing the country. Street protests dwindled, relations with the church were stable and Western Europe had decided to break the diplomatic quarantine of Poland begun after martial law.