After 15 months of debilitating political and economic crisis, Poland's communist authorities are beginning to consider what used to be the unthinkable: a final showdown with the independent Solidarity confederation of trade unions.

Throughout the Polish upheavals, declaring a state of emergency has been viewed as a prelude to national tragedy. The move has been talked about on several occasions, but immediately dismissed since it almost certainly would provoke retaliatory action by Solidarity in the form of a general strike.

Over the past few weeks, however, the political climate has changed. Attitudes on both sides have hardened as the economy disintegrates and the impatience of ordinary people with food shortages and inflation grows. What was once a disaster scenario is gradually becoming, for some Communist Party officials at any rate, a plausible political option.

In practical terms, the declaration of a state of emergency or martial law would mean the assumption by the government of dictatorial powers to direct the economy and crack down on political opponents. Soldiers could be drafted into factories and Solidarity's national leaders placed in detention. Strikes would be illegal and workers forced to obey orders as if they were in the Army. Civil liberties and the democratic reforms of the past year would be suspended.

Such extreme measures carry an enormous risk. If sufficient force were used, the workers might be cowed into submission. But a more likely result would be violent clashes and bloodshed that could only be resolved by foreign intervention.

The replacement of Stanislaw Kania as party leader by Gen. Wojciech Jaruzelski does not by itself bring such a final confrontation closer. Jaruzelski, after all, has been closely associated with Kania and is known to have opposed using the Army against Polish workers. What Kania's resignation does underline dramatically, however, is the failure of his brand of consensus politics to make any dent in Poland's enormous problems.

The road ahead is not clear. It may be that there is no way out, that it is impossible to square the aspirations of the Polish people with the ideological and security interests of the wider Soviet empire. But, for the first time since the Polish crisis began, the country's political leaders no longer seem to regard as sacrosanct the "line of agreement" proclaimed by Kania when he took office in September 1980.

That a state of emergency is being debated does not imply that it is imminent. There remains a wide gulf between contingency planning and the decision to act. The hard-liners in the party may be in the ascendancy, but the reformers probably are still strong enough to block such a radical change in policy.

The continuing stalemate in the party's leadership was reflected in a speech to the Central Committee by Jaruzelski following his appointment as first secretary. He tried to appeal to both factions simultaneously by insisting that the party would retreat no further, while reiterating an offer to broaden the ruling coalition to include more representatives of Poland's strong Roman Catholic Church.

An attempt, led by the conservative Warsaw Communist Party organization, to include a specific reference to the possible introduction of martial law was blocked after consultations with regional party chiefs. Instead, the hard-liners had to be satisfied with a vaguely worded passage in the resolution authorizing the government to take all necessary constitutional measures to save socialism in Poland.

The Central Committee meeting also was important in view of a long-running debate over the Communist Party's role in a reformed political system.

Six months ago, it seemed that the party was in the process of transforming itself into an organization very different from the traditional Soviet Bloc conception of a communist party. Reformist Communists hoped that the party itself would take the initiative in forcing the pace of democratic change in Poland, thus winning back public credibility and support. This in turn, it was argued, could lead to a new political stability based on cooperation between the party and Solidarity.

It was not only hard-liners within the party who were alarmed by this sudden upsurge of democratization. For years, Polish dissidents had based their political strategy on the assumption that the party could never be a vehicle for introducing reforms; instead, it should remain a kind of ideological fig leaf, acceptable to the Soviet Union, while providing a cover for the changes taking place in the rest of society.

In fact, the party's reformist phase proved short-lived. The significance of the latest Central Committee meeting is that the Polish Communist Party has reverted to type. Discipline and unity again are being lauded as supreme virtues, and party members who do not like it are being ousted. The growing division between "us" and "them" was illustrated by the decision to expel Bogdan Lis, a Solidarity leader, and Stefan Bratkowski, the independent-minded president of the Polish Journalists' Association, from the party.

At the same time, there has been a tightening in controls over the press. The party's propaganda chief, Stefan Olszowski, has declared an ideological struggle against "the enemies of socialism" -- and the battle is being waged with increasing intensity on radio and television. Solidarity's hopes of greater access to the mass media seem further away than ever.

Curiously, some of Solidarity's strategists are comforted by the party's change of heart. They argue that an all-out reformist party ran the risk of provoking a Soviet invasion, since the Kremlin would have little to lose. Their tactic is to attempt to limit the party's authority, rather than to reform it or take it over.

This is the central political battleground in Poland today. Solidarity wants to whittle down the party's power, and particularly its control over the economy and local government apparatus. The idea, in the words of one Solidarity official, is to reduce the party to the role of "the queen of England," a constitutional monarch who reigns but does not rule.

Needless to say, Poland's Communist Party is not prepared to accept such restrictions on its once unchallenged authority. Its new leaders, elected democratically at the extraordinary Party Congress in July, are young, ambitious, and eager to prove themselves. They do not feel responsible for mistakes committed by a previous generation of now disgraced politicians.

The new party leadership is eager to demonstrate that it is prepared to use all possible means to preserve its power. It is this new mood of assertiveness and sense of legitimacy that explains why, increasingly in Poland, the unthinkable is now being thought.