In a thinly veiled warning to the Soviet Union about Poland, leaders of the nine European Community nations today called attention to international principles of nonintervention in the affairs of other nations.

Ending a two-day summit meeting, the European heads of state did not mention the Soviet Union by name. They pledged, however, to conform to the priniciples of the United Nations charter and the 1975 Helsinski accord and suggested that others do likewise.

"The nine accordingly call upon all signatory states to abide by these principles with regard to Poland and the Polish people," the leaders said. "They emphasize that any other attitude would have very serious consequences for the future of international relations in Europe and throughout the world."

These consequences were not spelled out, and the overall intention of the European leaders appeared to be to make a firm but not provocative statement on the already tense situation in Poland. It had even been doubtful from the start of the summit whether the European chiefs would choose to make any political comment on Poland now.

British Foreign Secretary Lord Carrington called the statement issued today "a warning between the lines" that is "very clear."

The final statement included one page on Poland, which began by expressing "sympathy" for the country. But the European leaders soft-pedaled a common resolve to make available discounted surplus food by adding a sentence that avoided specific mention of such aid. It said simply, "[The European leaders] state their willingness to meet, insofar as their resources allow, the requests for economic aid which have been made to them by Poland."

The possibility of supplying excess butter and meat to Poland at below-market prices was reviewed by the European leaders during dinner last night. It is a politically delicate move in view of Soviet sensitivity to Western aid to Poland.

Community officials today said the sales would likely be made, though the exact amount, cost and timing would depend on hard-pressed Poland's ability to raise additional financing from individual European states.

While Polish diplomats in Brussels are known to have asked European Commission officials about the possibility of buying Western Europe's excess food stocks, Commission President Roy Jenkins told reporters that the Polish approaches so far have been "only tentative."

In general, this summit was noted for its lack of controversy. In the only other major action, the leaders gave the go-ahead for a fresh round of diplomatic contacts with Middle East nations to sound out opinion there on an extensive program of peace options prepared by European officials.

The move fell short of a new initiative and was seen as an action marking time until President-elect Ronald Reagan makes clear is own Middle East policy. At the same time, the new diplomatic mission, to be undertaken by the president of the European Council who will be from the Netherlands, was intended to show continued European determination to influence the Middle East peace process despite American and Israeli misgivings.

The relatively relaxed mood of this summit -- reinforced by the subdued surroundings of the offices for the meeting on a hilltop in this Central European duchy -- contrasted with the often stormy tone of other high-level European meetings earlier this year. Then, European leaders struggled over a response to the Soviet invasion of Afghanistan and a solution to Britain's budget problem.

Absent this time, too, was anything approaching the tense pitch reached when European chiefs in June challenged the U.S.-sponsored Camp David peace process by calling for the Palestine Liberation Organization to be associated with the Egyptian-Israeli talks on Palestinian autonomy.

At that time, the Europeans also launched a special diplomatic mission of their own to the Middle East -- undertaken by incoming European Commission president Gaston Thorn -- to gather ideas for possible new approaches to a comprehensive peace settlement.

The election of Reagan and the divisions and tensions within the Arab world brought on by the war in the Persian Gulf have stalled the European initiative. Hoping to keep it in play, European officials drew up an extensive options paper after the Thorn mission, and this document will be the basis for the new series of Middle East contacts.

The confidential paper is described by officials as a program of options rather than a peace plan. It is seen as the most comprehensive and detailed position the European Community has forged on a major foreign policy issue.

The document deals with the means of establishing Palestinian self-determination, Israeli withdrawal from occupied territories, security guarantees for the area and the future position of Jerusalem -- all major stumbling blocks in the Middle East peace process.

The justification for any European action is the mounting frustration here with the current Egyptian-Israeli impasse and the widespread view in European capitals that the Camp David principles are too narrow to encourage a negotiated settlement.

But a European initiative in the Mideast has had dubious worth in Washington's eyes from the start since Europe lacks the military weight to guarantee any solution in the region by itself and also does not have Israel's confidence.

Nonetheless, the European chiefs today called the recent Thorn mission a "success."