The European allies intend to seek closer consultations with the Carter administration and exercise more influence over the management of the linked crises in Iran, Afghanistan and the Middle East.

One goal of these contacts is to ensure that President Carter hears moderate outside voices while formulating U.S. policy, especially since the resignation of secretary of state Cyrus Vance, according to diplomatic sources at the summit meeting of the leaders of the nine Common Market countries here.

There European allies want only peaceful means pursued to gain the release of the American hostages held in Iran, a more flexible and coordinated allied policy in response to the Soviet invasion of Afghanistan, and more rapid progress on solving the problem of Palestinian self-determination as a key to peace in the Middle East, according to senior diplomats here.

They intend too use as channels of communications with Carter both bilaterial contacts, such as British Foreign Secretary Lord Carrington's visit to Washington next week, and scheduled meetings of allied diplomats and leaders such as the NATO council of foreign and defense secretaries in Brussels next month and the Western economic summit in Venice in June.

British Prime Minister Margaraet Thatcher said tonight that although the Venice summit would normally consist only of economic consultations among the United States, Canada, Japan, Britain, West Germany, France and Italy, "this time we will discuss wider subjects such as Iran, Afghanistan and the Middle East.

Thatcher, French President Valery Giscard D'Estaing and West German Chancellor Helmut Schmidt discussed the news of Vance's resignation at breakfast together here. Schmidt told West German reporters tonight that "regret in the circle of [ european] heads of government and foreign ministers about the resignation of Cy Vance is general."

Diplomats here refuse to be drawn out further in public on the implications of Vance's resignation, which Thatcher said was a matter "between him and the president." In contrast to Vance's reputation among the allies for quiet diplomacy and preference for negotiated solutions to problems, another Carter aide, White House national security adviser Zbigniew Brzezinski is often described as "confrontational."

To gain influence with Carter, several diplomats here said, European leaders must strongly support him after the aborted U.S. military mission to rescue the American hostages, despite the displeasure with its timing and their concern that its failure has only worsened the crisis. Many European diplomats also remain pessimistic that economic and diplomatic sanctions against Iran will really help.

But the communique issued by the nine European leaders at the end of the two-day summit tonight specifically reaffirmed last Tuesday's decision by the Common Market countries to impose tough economic sanctions on Iran if decisive progress toward the hostages' release is not made by May 17.

The communique and Italian Prime Minister Francesco Cossiga, the current Common Market president, declared the European leaders' solidarity with Carter and the American people in working for the hostages' release. But Cossiga also emphasized that this "should be sought by peaceful means."

Thatcher also drew the distinction between the failed rescue mission and other military measures. "When it comes to fighting or blockading," she said tonight, "that would be a totally different dimension and we would be opposed to that. That's why we are trying to pursue peaceful means.

Asked how the Common Market countries intend to convey this message to the Carter administration, Cossiga told reporters, "We have all the necessary diplomatic channels at our disposal to make the point known."

The European leaders also declared their "full support" for a new but unspecified diplomatic initiative that U.N. Secretary General Kurt Waldheim "intends to take to secure the release of the hostages."

"We wish to have a dialogue with the United States on harmonious implementation" of sanctions and diplomatic pressures on Iran to avoid a military confrontation there, said one senior European diplomat.

At the same time, like many other European diplomats here, he believes the Afghan crisis is much more important and threatening to the allies over the long run, "while from a psychological point of view, the hostage crisis is most urgent."

The European leaders reiterated their suggestion that a solution to the Afghan crisis "could be found in an arrangement which allowed Afghanistan to remain outside competition among the powers and to return to its traditional position as a neutral and nonaligned state."

This would require the Soviet Union's withdrawal of its troops there in exchange for an international guarantee of Afghan neutrality "respecting the right of the Afghan people freely to determine their own future." The European leaders invited Islamic and nonaligned nations to join them in pressing this initiative.

Finally, the European leaders agreed here on the importance of solving the question of Palestinian sefl-determination as a means of achieving a "comprehensive, just and lasting settlement" between Israel and its Arab neighbors. European diplomats believe that this could be a key to easing tensions throughout the Middle East, Persian Gulf and southwest Asia.

The European leaders reportedly were concerned about reports from French diplomats here of the "extreme toughness, of the Soviet Union's position on Afghanistan and "the Soviet will to deal with the United States in a very agressive manner," demonstrated in Soviet Foreign Minister Andrei Gromyko's recent talks with French Foreign Minister Jean Francois Poncet in Paris.

But large differences remain between the Europeans and the Carter administration on how to deal with the Soviets.

Diplomatics sources said these issues and the need for much better consulation on them between the United States and the European allies will be discussed within Europe and in bilateral contacts with Washington in preparation for the NATO meeting of foreign and defense ministers May 13 and 14 in Brussels.