The Polish Communist Party leader, Stanislaw Kania, warned the country's new independent trade unions today against establishing a poltical power center to rival the ruling Communist Party.

In a speech that combined tough words with conciliatory appeals, Kania called on rank-and-file Communists to unite to defeat the forces of anarchy and chaos. He insisted that political and social reforms introduced in Poland during the last few months are irreversible, but said the process of renewal is threatened by "antisocialist" elements.

It was not immediately clear to whom he was referring, but similar allegations have been made in the past against dissident groups including the activist Committee for Social Self-Defense led by Jacek Kuron, who is now one of the main union's principal advisers.

Kania's remarks, made at the start of an important two-day plenum of the Central Committee, appeared partly designed to reassure the Kremlin of the Communist Party's ability to control events here. But he also criticized hard-liners within the party who refused to cooperate with the independent Solidarity union federation.

During his 70-minute speech, later broadcast in full on state television, Kania revealed that Poland recently received $1.3 billion in hard-currency aid from the Soviet Union, as well as special supplies of commodities and raw materials. The size of the figure, which surprised Western analysts, underlined the extent of Moscow's commitment to the political and economic stability of this key Soviet Bloc state.

Kania said financial assistance has also come from the West, but made no mention of the $3 billion loan Poland is reported to be seeking from the United States.

During almost three months as party leader, as successor to the disgraced Edward Gierek, Kania has attempted to steer a middle course in Polish politics. His latest speech, delivered on behalf of the ruling 13-member Politburo, also represents a compromise between the entrenched interests of the still-powerful party apparatus and the demands for more rapid change being voiced by the party's rank and file.

The speech reflected the fact that the new Polish leadership is caught between the conflicting demands of Moscow and Solidarity. As Kania is finding out, it is difficult to satisfy the hopes of the Polish people for reform and yet to allay Soviet fears that liberalization might get out of hand.

Kania disclosed that more than 500 party and government officials at various levels have been dismissed since the wave of strikes last August that resulted in the setting up of independent unions. The purge of corrupt and incompetent officials will continue, he said, but he rejected calls for fresh elections to all party bodies.

The strongest passage in his speech came when he condemned what he described as political strikes staged by Solidarity. It is widely assumed here that Kania's own position as party leader has been weakened as a result of continuing labor unrest and particularly by demands of Solidarity's Warsaw branch last week for reduction in the power of the security services.

In an apparent effort to bolster the reformist faction in the party leadership, Solidarity leader Lech Walesa reminded his supporters in a weekend speech that strikes should only be regarded as a last resort.

Kania accused "antisocialist elements linked to imperialist circles" of helping workers strike to create a springboard for their own activities. "These attempts are counterrevolutionary and against the workers' interests," he said. "Anarchy is easy to create, but very difficult to control. It is high time we sobered up."

Kania announced that an emergency Communist Party congress will be held between March and April 1981.This decision will disappoint reformists in the party who have called for a congress as swiftly as possible to draft an entirely new party program and elect a new Central Committee.