One of Poland's more controversial politicians, Mieczyslaw Moczar, was reelected to the ruling Politburo tonight as the Communist Party sought to bolster its dwindling authority.

Moczar's return to the Polish leadership, after nine years in the political wilderness, coincided with the dismissal from the Central Committee in disgrace of the former Communist Party chief, Edward Gierek. Four Politburo members closely associated with Gierek's rule also resigned from the Politburo.

Western analysts interpreted the changes as essentially strengthening the new leadership's moderate policies. The return of Moczar, regarded as an authoritarian politician, was balanced by the election to the Politburo of Tadeusz Grabski, an outspoken reformist.

A former interior minister, Moczar, 67, led a campaign against Jewish influence in Poland in the late 1960s and has the reputation of being an outspoken nationalist. In recent months, however, he has tried to project a new image for himself as a strong politician with clean hands who stands ready to prevent the country's drift toward chaos.

His appointment to the Politburo reflects the delicately balanced political coalition shaped by the new Polish leader, Stanislaw Kania, who succeeded Gierek three months ago. The latest personnel shake-up came at the end of a two-day plenary session of the Polish Communist Party's Central Committee, which met against the background of heightened speculation in the West about possible Soviet intervention here.

Another noted reformer, Tadeusz Fiszbach, the regional party boss in Gdansk, was appointed a candidate member of the Politburo. His election is likely to please grass-roots party organizations, which have become increasingly restless in their demands for greater democracy and decentralization.

Another sign of the party's continuing commitment to reform -- despite Moscow's misgivings -- was provided by the election of a commission headed by Kania to prepare for an extraordinary party congress to be held around March 1981. As the party's supreme organ, the congress will have the task of approving an entirely new political program.

Despite the concern expressed in the West, there is little obvious tension here among either officials or ordinary poles about reported troop movements on the country's borders. Many Western analysts in Warsaw believe that, while a Soviet invasion cannot be ruled out in the long term, at present the Kremlin is still seeking to influence the policies of the Polish leadership and warning the Polish people of the dangers of pushing too far.

Together with the calls for a deepening of the "renewal" process, the meeting also heard strongly worded warnings against "counterrevolution" and "imperialist subversion." A relatively tough line was taken by many speakers, including such noted reformers as Mieczyslaw Rakowski, editor of the weekly magazine Polityka.

One of the most outspoken speeches during the debate came from the interior minister, Miroslaw Milewski. He said the young independent trade federation Solidarity had been infiltrated by antisocialist elements who wanted to use the union for their own purposes.

"There are quite a few people hostile to socialism in Poland," Milewski said. "They attach definite calculations and hopes to the creation of a state of tension and anarchy. Some of them, in close cooperation with imperialist intelligence services and subversion centers, have attempted to implement a program of overthrowing the state and taking over power in Poland.

The deputy defense minister, Gen. Jozef Baryla, told the meeting that the Army supported the process of political reforms. However, he also warned of the danger of counterrevolution resulting from economic disorders, political anarchy, and chaos.

Baryla said propaganda had been stepped up in the Army, in cooperation with other Warsaw Pact countries, with the aim of improving its combat readiness. Hinting at a possible role for the Army in the event of a breakdown of law and order, he said the armed forces were an important element of communist power in Poland and would faithfully defend the state.

Meanwhile, Rakowski expressed concern at what he described as the increasing influence of radicals and anarchic elements in Solidarity. In an apparent reference to the dissident Committee for Social Self-Defense, he said "political enemies" of the Communist Party were now acting as advisers to some of the union's leaders.

Instead of a last resort, strikes had become a normal method of behavior for the union, he said.

Such remarks have helped give a markedly different tone to the present meeting when compared with the last Central Committee session two months ago. Then the reformists were in ascendancy with their demands for a purge of discredited politicians responsible for leading Poland into crisis.

The political scene has been transformed, however, during the last two months as a result of the mounting economic problems, Solidarity's increasing militancy and the war of nerves being conducted by Poland's Soviet Bloc neighbors.

The tougher rhetoric at this Central Committee meeting appeared partly designed to reassure Poland's worried Warsaw Pact allies of the party's determination to exercise its authority despite continuing industrial unrest. But it will also serve as a reminder to Solidarity's leaders of the limits beyond which they must not cross.

Meanwhile, Polish newspapers today reported more details of the Soviet aid package of $1.3 billion revealed by Kania in his address to the Central Committee yesterday. The aid, which will be made available during the coming year, is made up of $1.1 billion in hard-currency credits and $200 million worth of commodities.

An official communique said Poland was free to use the credits as it wished, either to pay the interest on its huge hard-currency debt to the West or to finance additional imports of foodstuffs or raw materials.