West European leaders toned down criticism of the Reagan administration in a joint statement issued today amid hopes that the gesture would encourage quiet diplomatic efforts to resolve transatlantic strains over new U.S. sanctions against the planned Soviet gas pipeline to Western Europe and other recent American trade actions.

This moderate tack was pressed by British Prime Minister Margaret Thatcher against French President Francois Mitterrand, who wanted a harder public line against the United States to come out of the two-day summit here of the 10-member European Community.

The British view was that to continue an abrasive public tone toward Washington would not help Europe's private diplomatic attempts to gain reversal of the pipeline sanction and tariffs on U.S. imports of European steel and agricultural products.

Speaking to reporters at the end of the summit conference, British Foreign Minister Francis Pym said the appointment of a new U.S. secretary of state also played a part in concluding that too much overt criticism would be "both unnecessary and unwise."

The European leaders also took a relatively mild stance on the battle in Lebanon, which was the other topic dominating their meeting. They called for a cease-fire, to be accompanied by the immediate withdrawal of Israeli forces "from their positions around" Beirut and the "simultaneous withdrawal of the Palestinian forces in West Beirut in accordance with procedures to be agreed between the parties." This amounted to a watered-down version of a French plan, favored by the Palestine Liberation Organization, that would move PLO guerrillas to several Lebanese camps and establish a neutral buffer zone in and around Beirut.

No mention was made, however, in the European Community statement of what to do with PLO armaments or to where exactly the PLO should withdraw. Disputes on both these points between the PLO and Israel are a key obstacle to obtaining a stable cease-fire.

As for any future role of the PLO in the Middle East peace process, the Europeans stuck protectively to language they had agreed to two years ago at their Venice summit, reasserting that the PLO "should be associated" with negotiations on solving the Palestinian problem. Both Israel and the United States have refused to accept PLO involvement in the peace process.

The two-page statement on Lebanon included only one sentence condemning Israel for invading. Economic sanctions were said by senior European officials not to have been considered in the meeting.

An embargo on European arms shipments to Israel was discussed but not formally adopted because, according to Wilfried Martins, the Belgian prime minister and current chairman of the EC council, "it was discovered that member states have not in fact been selling arms to Israel."

Taking a minimal slap at Israel, the leaders announced suspension of a ministerial meeting on cooperation between the community and Israel that was due to be held in Brussels next week. They also postponed the signing of a second financial protocol with Israel that would involve aid of about $46 million over five years.

The mild language and action against Israel appeared to reflect reluctance on the part of some West European countries, particularly West Germany and the Netherlands, to mount a European initiative at a time of intense conflict in the Middle East. West German Chancellor Helmut Schmidt was quoted by a spokesman as telling the community's Council that the role of Europe in the Middle East must not be overestimated given the lack of European leverage on events there.

On relations with the United States, the European leaders made clear their concern had not lessened--even if they had lowered their voices--over what they still view as unfriendly, unlawful and unacceptable U.S. action. Their major objection was clearly to Reagan's extension of the ban on using U.S.-developed technology in the Soviet gas pipeline. The ban now covers European firms working with U.S. licenses that have already signed contracts with Moscow for the project.

Mitterrand, at a press conference spelling out his objections to the new pipeline sanctions, said he had wanted stronger language against the United States in the final joint European statement. He attacked Washington for violating compromises reached at the seven-nation economic summit at Versailles earlier this month and for demonstrating "a grave lack of solidarity" with its allies.

"We can't just take these meetings and turn them into a means of propaganda for each of the participants," Mitterrand said. "If so, it's not worth continuing them." The French leader added that while the U.S.-European dialogue has not been interrupted, "let's just say there has been too much American monologue."

The final community statement on transatlantic relations said Europe would observe the Versailles agreement. In its one mildly critical passage, it warned the United States "that the maintenance of the open world trade system will be seriously jeopardized by unilateral and retroactive decisions on international trade, attempts to exercise extraterritorial legal powers and measures which prevent the fulfillment of existing trade contracts." The statement expressed "concern at these recent developments which could have adverse consequences for their relations with the United States."