Soviet leader Mikhail Gorbachev arrived here today, and Polish officials hinted at a new initiative to release political prisoners on the eve of a communist party congress expected to reaffirm the leadership of Gen. Wojciech Jaruzelski.

Dressed in a brown civilian suit, Jaruzelski met Gorbachev and Soviet Foreign Minister Eduard Shevardnadze at Warsaw's airport this evening in a low-key kickoff to a visit widely interpreted here as a show of Soviet confidence in the Polish leadership. Gorbachev, paying his second visit to Warsaw since becoming Soviet party leader, also attended the East German party congress in April but skipped the party meetings of Czechoslovakia and Bulgaria.

In sharp contrast to the Soviet leader's high-profile trips to East Berlin and to Hungary earlier this month, Polish media gave no advance announcement of the visit and television news gave a minimum of coverage to the arrival ceremony tonight. Political observers here said Gorbachev, who reportedly will address the congress Monday, may adopt a more aloof approach to Poland, where longstanding anti-Soviet feelings were recently boosted by the Chernobyl nuclear accident, which created higher than normal radiation levels here.

Security forces have blanketed Warsaw since yesterday, lining the road from the airport and stopping cars for inspections at many points around the city. Lech Walesa, leader of the outlawed union Solidarity, and other top opposition leaders have been repeatedly summoned for interrogations and warnings this week in an apparent effort to head off any show of internal opposition during the congress.

At the same time, a top party official tempered the get-tough atmosphere at a press conference today by announcing that the communist-backed Movement for National Rebirth had proposed a new initiative to release political prisoners. Such formal proposals have been the first step in previous amnesties under Jaruzelski's rule.

Stanislaw Ciosek, the head of the party Central Committee's department handling internal security, told western reporters that details of the prisoner release "will be published in due time." Suggesting that any amnesty would depend on the congress' evaluation of the internal situation, he refused further comment.

The five-day gathering of the Polish United Workers Party has been planned by top leaders to appear quiet, businesslike and devoid of the upheavals that marked the last congress in July 1981, in the midst of the party's 16-month standoff with Solidarity.

"The idea is the congress will reflect the times we are in, and this, for us, is the time of peace and normalization," one senior official said.

Jaruzelski, who will address the congress Sunday, is expected to emphasize the beginning of a "second stage" of his program of economic reforms. Western diplomats said rules calling for multiple candidates for the party leadership as well as secret balloting, introduced at the stormy 1981 congress, will probably be quietly scrapped, allowing Jaruzelski to win reelection as first secretary and carry out several changes in the ruling Politburo without incident.

In the last weeks before the congress, party officials appeared to mount a major propaganda campaign to appease populist sentiment that remains well-rooted in the party's rank and file even though most of its spokesmen have been purged from top positions.

Jaruzelski promised action against Poland's "super-rich," in his last major speech before the congress.

Both Interior Minister Gen. Czeslaw Kiszczak and his deputy, Gen. Wladyslaw Pozoga, were granted much media attention for attacks on the opposition and the Reagan administration.

The security forces scored a major success with the arrest three weeks ago of Solidarity underground leader Zbigniew Bujak and national media have since emphasized an account of the Polish opposition as little more than an elaborate espionage operation backed by the United States.

Detentions of activists have surged and church human rights sources say more than 300 political prisoners are now being held.