Poland's acute economic problems and the weakening of moderate leadership within both the Communist Party and the independent Solidarity trade union have combined in recent weeks to produce a dangerous new phase in the country's continuing political crisis.

Where previous rounds of brinksmanship ultimately have resolved themselves in a pattern of reconciliation and hard-won compromise, there is a feeling here in the current test of wills that the stakes are much higher and that the Communist Party is determined to make the most of what it sees as its last chance to keep its grip on political power.

Some Houdini-like solution may yet emerge, but it is the combination of bluff and threat, and the unclear line between them, that makes the present phase of Poland's crisis so dangerous and so crucial.

During the past two weeks, both Solidarity and the authorities have dug themselves into positions from which it is very difficult to retreat. The Communist Party leadership, supported by the Kremlin, has made clear its belief that the union has become a "counterrevolutionary" organization with which dialogue is now impossible. Solidarity has demanded that the party give up control over the economy and agree to free elections, which could eventually result in the party's own annihilation as a political force.

A few months ago, there was still a good chance that reformers within the party would be able to make a deal with moderates in Solidarity. An independent trade union representing millions of workers was obviously incompatible with the traditional concept of a Communist state in which all power is concentrated in the hands of the party. But it did seem possible that the party could somehow reform itself to accommodate the new political structures, and that in return Solidarity would accept certain limits on its activities.

Today that dream-- of a "democratic socialism" that has inspired reformers throughout Eastern Europe--seems further away than ever.

The massive, and apparently well-coordinated, propaganda campaign against Solidarity has included statements from the ruling Politburo and government and a Kremlin protest against the "rising tide of anti-Sovietism" in Poland. Television news carries nightly denunciations of Solidarity for pushing the country toward disaster and pledges by uniformed Army officers "to defend socialism as we would defend Poland."

As was no doubt the intention, all this has had a psychological effect on ordinary Poles. Privately many people express worries about the country's future and, for the first time, the real fear that Poland's experiment in democracy may after all end in bloodshed. By contrast, at Solidarity headquarters in Warsaw, a kind of relaxed good humor prevails as if to say, "We've all been through this before."

There are, however, important differences between the latest round of sabre-rattling and previous crises such as that triggered by alleged police violence against Solidarity activists in the northern town of Bydgoszcz in March. This time the issues are much closer to the central question of political power in Poland.

Secondly, in the government's view at least, months of worsening economic crisis have limited Solidarity's freedom of action. The union's main weapon, the strike, has a double edge. If all it produces is greater economic chaos then Solidarity members themselves are likely to suffer. The authorities clearly hope that the hardships of everyday life have blunted Solidarity's popularity and the nation's will to resist.

Finally, at the time of the Bydgoszcz incident, the forces for moderation in Poland were still very strong and--as it turned out--able to impose their will on events. Today they are weaker and disillusioned. Cardinal Stefan Wyszynski, who played an important mediator's role back in March when there was the threat of a general strike, is dead, and his successor does not wield the same authority. The prime minister, Gen. Wojciech Jaruzelski, has proved to be a weak administrator unable to impose his will on either his own apparatus or on Solidarity. And Solidarity's own leaders are being pushed by their members into taking ever more radical positions.

During any revolution, the political center is difficult ground to occupy. The moderates find themselves attacked from both sides and, sooner or later, it becomes difficult to resist the pull of one or other polar force. This is what seems to have been happening in Poland.

Reformers in the party underestimated the Soviet Union's capacity for thwarting political change here. They harbored the illusion that they would be left to themselves to get along with Solidarity. Their mistake was that they ignored the fact that, in the last resort, it is only thanks to Soviet support and military might that the Communist Party is able to remain in power in Poland at all.

With hindsight, it is now clear that the Soviet letter sent to the Polish party back in June had a much greater impact than originally believed. It failed to topple the party leadership, but it achieved a more important objective: the blocking of major policy changes at the extraordinary party congress in July. Despite the democratic election procedures, the reformers were a minority and some were even dropped from the Central Committee.

On Solidarity's side, radical political solutions have become more attractive as the country's economic plight has worsened. In order to exist at all in a one-party state, Solidarity was unable to limit itself to just being a trade union. It had to become a social movement, or, as the party leadership alleges, a political opposition.

Compared with six months ago, fewer people believe it can all end well. This is not to say that all hope has been lost. But there do seem to be fears deep in the national psyche that make a permanent compromise between the communist state and an independent union very difficult to achieve.

In the West, preoccupation with the threat of a Soviet invasion of Poland has tended to obscure other, more immediate dangers. One is that the Soviet Union could cut off economic assistance to Poland, including deliveries of subsidized oil and other raw materials, thus virtually strangling the Polish economy. Another is that the Polish authorities could clamp down on Solidarity, closing its publications and refusing to make any more concessions.

In the last resort, the authorities could still make use of the enormous machinery of state repression: the armed forces, the police and the half-million-strong party and local government apparatus. That, in turn, could lead to civil war and, finally, a Soviet intervention.

The other possibility, still believed in by many Solidarity activists, is that both the Kremlin and the Polish party are bluffing. The Communists, so this argument runs, have lost Poland, and will sooner or later be forced to recognize it.

The party evidently believes that this is its last chance to establish its credibility, to prove that it has the strength and the will to remain in power. Solidarity fears that, if it allows itself to be forced onto the defensive now, it could gradually be pushed back and, little by little, be made to relinquish its gains.

At present, there is still an atmosphere of "phony war." The weapons remain the old ones of political rhetoric, resolutions, verbal ultimatums and threatening allusions. But both sides are maneuvering for position.

Recently a distinguished Polish journalist described a conversation with a colleague from East Germany who expressed sympathy for the Polish experiment but said the Poles lacked the discipline to see it through. It would take a nation like the Germans, with their Prussian thoroughness, to make it work.

The Pole commented: "That's probably true. But then the Germans wouldn't have had the imagination to start it. We'd still be no nearer reaching our dream of democratic socialism."

And he added gloomily: "Perhaps it's impossible anyway, perhaps it's just a contradiction in terms."