Poland's Communist Party leader, Stanislaw Kania, has faced down the open challenge to his position mounted by pro-Soviet hard-liners

In a closing speech to a stormy Central Committee meeting that was published today, Kania pledged to maintain his conciliatory line toward the independent Solidarity trade union federation.

At the same time, he attempted to defuse Soviet concern about developments in Poland by promising tighter controls over the mass media and a strengthening of the Army and security forces. A resolution issued after the two-day meeting also called for stronger discipline in the Communist Party's own ranks.

The consensus among political analysts here is that Kania, who became Communist Party leader 10 months ago following the ouster of Edward Gierek, proved himself a highly skillful politician in facing down a determined effort to unseat him by the hard-line faction in the party. What is more, he survived with his policies more or less intact, despite a strongly worded Soviet letter demanding a halt to Poland's internal reforms.

Despite the misgivings of many conservative Central Committee members, who sense the approaching end of their political careers, a special congress of the Polish Communist Party will go ahead as scheduled on July 14 -- barring new upheavals.

In his concluding speech, Kania said all Politburo members and Central Party secretaries should be elected as delegates to the congress for the sake of continuity and in order to preserve party unity. Until now, only a handful of party leaders have been elected and it is stil unclear where the rest, Kania included, will stand.

Unless the system of elections is changed, there is a very real chance that several present members of the Politburo may not even be chosen as delegates.

In its final resolution, the Central Committee ignored calls by some of its members for the annulment of elections of delegates already chosen for the congress. Of the 428 delegates elected so far -- out of a total of 2,000 -- a clear majority are strongly committed to the adoption of major economic and political reforms.

Two-thirds of the delegates are intellectuals rather than workers, to the Kremlin's disgust and Kania's own professed alarm. Most are new faces and a sizable proportion, 130 so far, are Solidarity members.

In his final speech, Kania also insisted that political methods alone be used to resolve the crisis. Several Central Committee members had called for the abandonment of this line while at the same time implicitly countenancing the use of force against Solidarity. Their argument appeared to be that, if Polish Communists did not take a tougher line, the Soviet Union might do the job for them.

This theme was expressed by one Central Committee member who, no doubt unwittingly, echoed the phrase made famous by "The Godfather" in his description of the Soviet letter: "This Soviet Union has made us an offer we can't refuse."

In Washington, the U.S. State Department had accused the Soviet Union of interfering in Poland's internal affairs by sending the letter.

[The charge was contained in a statement that said in part: "The threatening tone of the recent letter from the Central Committee of the Communist Party of the Soviet Union, a text of which had just become available, amounts in or view to interference in the internal affairs of Poland."]

The quetion now is whether the Soviet leadership will accept the outcome of the Polish Central Committee session. The choice facing the Kremlin is stark. Either it allows the congress to take place as planned in five weeks' time and tolerates the markedly different kind of Communist Party that is likely to emerge as a result, or it intervenes directly in Poland with all the risks and dangers such a move would involve.

Much is still unclear about how Kania managed to turn the tables on his hard-line opponents. At one point, the tide of opinion appeared to be running strongly against him, with 15 out of the first 18 speakers favoring changes in the ruling Politburo.

Kania evidently used a recess following an attack on his leadership by a fellow Politburo member, Tadeusz Grabski, to his own advantage, securing the support of both the Army and the 49 provincial secretaries. Then Kania successfully insisted on an open ballot.

During the first round of voting on a procedural motion, a majority of the Central Committee abstained, apparently waiting to see who would emerge on top. The second round decisively Kania, with 24 members in favor of holding a vote of confidence in the Politburo and 84 against.