Poland's ruling Communist Party sought today to close ranks behind the martial law chief, Gen. Wojciech Jaruzelski, in an attempt to heal its divisions and regain political credibility.

A two-day session of the policy-making Central Committee--the first since the military crackdown--was dominated by calls for harsh action against political opponents. But Central Committee members also voiced demands for a cleansing of the party's own ranks and an end to factionalism.

Despite earlier reports of dissatisfaction among party hard-liners, there was no sign of an open challenge to Jaruzelski or to the centrist group with which he is associated. His political position is now seen as virtually impregnable as long as martial law continues and the Army controls the country.

Soviet press reports of the Central Committee meeting suggested that the Kremlin places top priority on rebuilding a united Polish Communist Party--and this is likely to have helped Jaruzelski fend off internal dissent. The fact that his forthcoming visit to Moscow was announced well in advance of the meeting is seen here as a calculated gesture of support from a grateful Soviet leadership.

The implicit Soviet support for Jaruzelski has strengthened his hand against the party's left wing, which had been demanding a purge of moderates on the Central Committee. A document circulating among hard-liners prior to the plenum called for the dismissal of some of Jaruzelski's closest advisers including Deputy Premier Mieczyslaw Rakowski.

Several leading speakers at the Central Committee meeting called for an end to "factions" and "clubs" operating outside the party's legal structures. This was seen primarily as a move against the hard-line element, which has organized Marxist-Leninist discussion clubs around the country.

Although well-organized and vocal, the party's leftists at present do not seem to have a majority on the Central Committee. Their main strength is that they advocated a showdown with the independent trade union movement Solidarity long before this became the official party line. Events, they feel, vindicated their stand.

The head of the party's control commission, Jerzy Urbanski, said all activities outside the party's recognized structures were evidence of a lack of unity. He demanded an end to "all factional activities no matter what the motivation."

His warning was echoed by Edward Kazimierski, a worker on the 200-member Central Committee, who said: "I can't imagine that now when we all struggle for party unity that there can exist factions. Today's meeting should put an end to all factions existing in our party."

It is generally believed that the party hard-liners eventually would like to replace Jaruzelski as party leader with someone like Stefan Olszowski, the secretary in charge of propaganda. In that event, Jaruzelski might be given a largely honorary position such as president or marshal of the armed forces, leaving Olszowski real political power.

The hard-liners are also believed anxious to disgrace former party leader Stanislaw Kania, who advocated a moderate stance toward Solidarity. Kania has been dropped from the Politburo but remains a Central Committee member.

Despite Jaruzelski's apparent success at this meeting, the hard-line element in the party remains strong. It found expression in several speeches calling for stronger action against dissidents.

Zbigniew Hanff, a rescue worker at a Silesian coal mine, complained that--despite martial law--there were still many instances of antigovernment leaflets being distributed and industrial sabotage.

"Enough of this," said Hanff. "The enemy must be isolated once and for all. We must get to the very core of the problem."