The leaders of Poland's rival power centers -- Communist Party chief Stanislaw Kania and Lech Walesa of the new independent trade union movement -- met here this evening for the first time amid mounting concern about the country's economic problems.

Walesa, who led a wave of strikes against the government in August and September, has had several meetings over the past few weeks with senior government officials, including Prime Minister Jozef Pinkowski, but his meeting with the party leader, the most powerful figure in any communist state, is symbolic confirmation of Kania's determination to treat Walesa's Solidarity trade union organization as a partner in extricating Poland from its political and economic difficulties.

The meeting at party headquarters, during which the two men talked for 90 minutes with only secretaries present, came just four days after the Supreme Court defused a potential confrontation with the government by providing a compromise solution to a dispute over the statues of the new union organization.

Afterwards, Walesa told reporters: "I was surprised at the first secretary's [Kania's] sincerity. It was a good meeting. We each raised the problems that were of most concern to us."

Undoubtedly the issue of most concern to the government right now is how to overcome the country's desperate economic problems at a time of rising consumer discontent caused by widespread food shortages.

In a statement to the Polish news agency PAP, the minister of food industry, Jan Zaleski, said that food exports had virtually been halted. It was also disclosed that Poland would be buying large quantities of meat and sugar from abroad in addition to grain purchases made earlier this year.

Shortages of meat and other basic items were one of the main grievances voiced by workers during last summer's round of labor unrest. Since the end of the strikes, Polish housewives have complained that supplies in shops have worsened rather than improved and more time is wasted standing in line than before.

The decision to curtail food exports illustrates the complexity of the task facing the government. Traditionally, exports of agricultural goods such as ham and bacon have helped pay for the charges on Poland's foreign debt, which now stands at around $21 billion.

In August, government negotiators successfully resisted workers' demands that no food products be exported unless the home market had been fully satisfied. Deteriorating supplies and mounting frustration among ordinary Polish families have evidently forced the authorities to do what they refused to do just three months ago.

According to reports from Washington, Poland has asked for $3 billion in U.S. economic aid. The size of the request, which comes as little surprise to foreign diplomats in Warsaw, underlines that Poland relies as much on the West as on its Soviet bloc allies to help it out of its present difficulties.

Although the Soviet government pledged support during talks with Polish leaders in Moscow earlier this month, the Soviet Union and other Eastern European countries have neither the desire nor the ability to pick up the tab for all of Poland's economic burdens.

Thus, whatever the strains in detente, and however great the ideological reservations of countries like Czechoslovakia and East Germany, it would be virtually impossible for Poland to cut its links with the West.

The British trade minister, Cecil Parkinson, who is visiting Warsaw, said he believed that Poland's most recent requests for economic assistance had not be directed to the United States alone, but to Western countries in general.

Polish officials said that, in order to help alleviate shortages, Poland would be importing 50,000 tons of meat and 100,000 tons of sugar from Cuba in the near future. The ruling Politburo has approved a plan to introduce meat rationing, another demand of striking workers.

Another problem facing the government is that, as a result of last summer's strikes, most Poles have received substantial pay increases. The inevitable result of too much money chasing too few goods has been longer lines outside shops.