Sharp differences among European, Japanese and American officials on how to deal with international trade issues were discussed fully and openly during a three-day session of the Trilateral Commission which ended here Tuesday evening, conference chairman David Rockefeller said at a concluding press conference yesterday.

The Trilateral Commission -- a target of bitter criticism from both right-wing and left-wing groups -- is a private organization formed in 1972 to identify major problem areas and offer ideas on how to handle them, Rockefeller said. He noted that one especially important result had been to involve Japan more fully in Western European-North American economic dialogues.

On the specific issue of Japanese car exports to Europe and North America, Rockefeller said that Americans at the conference has spoken in favor of some form of restrictions, while the Japanese "naturally were not anxious" to accept a protectionist solution.

On another key issue, Georges Berthoin, European chairman of the Trilateral Commission, told reporters that there is "a growing perception" among European officials that "economic summits [among heads of state] should not only tackle economic issues, but broader political issues as well." The future structure of economic summitry is expected to be widely discussed in advance of, and at, the seventh heads-of-state summit in Ottawa in mid-July.

Other sources said that the most vigorous protectionist case on autos was not made by any Reagan administration official in attendance, but by commission member Philip Caldwell, chairman of hard-pressed Ford Motor Co. But concern over going this route was expressed by Marina von Neumann Whitman, vice president and chief economist of General Motors Corp.

Sources also said that at least some Japanese participants criticized the extent to which Japanese car producers had been pushing car exports, and one indicated a belief that it was time for the Japanese industry to accept voluntary restriction.

The Reagan administration still hasn't formulated a final policy position on the auto question. But a medium-level interagency team is scheduled to go to Tokyo this weekend to begin informal discussions with Japanese officials.

Japanese sources at the Trilateral Commission indicated that there is about as much division between the Ministry of International Trade and Industry on how to deal with the touchy auto problem as there is in the American Government.

The future of economic summits was one of the themes of a paper on multilateral issues by Miriam Camps of the Council on Foreign Relations. While Takeshi Watanabe, Japanese chairman of the commission, broadly endorses Berthoin's view that summits should leave more of the economic problems to the International Monetary Fund and similar agencies and concentrate on political-cumdefense issues, the idea gained only lukewarm approval from Rockefeller. The American said he thought giving additional scope to summits "might sidetrack [other] normal communications."

Another major paper discussed at the sessions, on Middle East problems, raised the question of how to deal with the Palestine Liberation Organization as a political force. Rockefeller observed that although the "reality" of the PLO could not be denied, its refusal to reorganize the legitimacy of Israel's existence provided little hope that the PLO would gain international acceptance.

Berthoin added that one good result of the paper and the Trilateral discussion of it was a better understanding by the European side of "the fundamental importance" of the Camp David agreements, and a better understanding by Americans present of the European desire to play a role in the Middle East peace-making process.

At different points during the meeting, the commission met with Vice President Bush (before Monday's assassination attempt on the president), Defense Secretary Caspar Weinberger and Secretary of State Alexander Haig.