North Atlantic Treaty Organization defense ministers today sent President Reagan their strongest message yet on the need to submit a new proposal to the Soviet Union for reducing the number of medium-range nuclear missiles deployed in Europe.

"Everybody has the feeling that there must be some movement in the Geneva negotiations," said Dutch Defense Minister Job de Ruiter in describing the closed sessions of the NATO defense ministers who are meeting here as the Nuclear Planning Group.

A U.S. official briefing reporters acknowledged that the "consensus" among European defense ministers is that something short of Reagan's zero-option proposal must be presented at Geneva. The zero option calls for the United States to forgo deployment of 108 Pershing II and 464 cruise missiles in Western Europe in exchange for the Soviet Union retiring its 351 SS20 mobile missiles and older medium-range missiles.

"There is a consensus that an interim agreement on the way to zero could be a useful thing," said the U.S. official, who could not be identified under the ground rules of the briefing. Stressing that it will be up to Reagan to decide whether to offer an interim proposal, the official said of the discussions here: "No one said, 'For God's sake, we've got to do something tomorrow.' "

European defense ministers interviewed between the secret sessions at this seaside resort, went to unusual lengths to explain that they suggested rather than demanded that Reagan back away from the zero option, at least temporarily.

NATO Secretary General Joseph Luns helped unleash this additional pressure--however gently expressed--by declaring in a Belgian television interview Sunday that the zero option was "not attainable."

The Luns statement "was not helpful," a U.S. official said. He added: "To say it's unattainable now may not mean it's unattainable later."

In contrast to some past NATO sessions, Defense Secretary Caspar W. Weinberger did not take on fellow defense ministers in heated debate as they urged a change in President Reagan's position, according to people who saw him in action here. Instead, Weinberger assured the defense ministers that Reagan already was considering an alternative missile proposal and was interested in the views of NATO allies.

Reagan is scheduled to make a major speech Wednesday night to try to build support for his defense budget. U.S. officials in the Weinberger party said the version of the speech they had read did not disclose any alternative missile proposal.

While acknowledging that the zero option was challenged here, U.S. officials said there were several positive developments in the first two days of this Nuclear Planning Group meeting. They said that in urging an interim proposal the European defense ministers agreed that Reagan's conditions for such an agreement must be met.

These conditions, a U.S. official said, include "equal forces on both sides" in medium-range missiles; no distinction between Soviet SS20 missiles aimed at Europe and those trained on China; no inclusion of the nuclear strategic forces of Britain and France; no restrictions on U.S. contributions to NATO conventional forces, and an agreement that is verifiable.

U.S. officials also hailed the widespread support here for deploying Pershing II and cruise missiles on schedule. The 108 Pershing II missiles, which are to replace the same number of Pershing I missiles already in West Germany, are scheduled to be deployed this December. Britain is scheduled to receive the first of 160 cruise missiles the same month.

Of the remaining 304 cruise missiles, 96 are planned for West Germany; 112 for Italy and 48 each for Belgium and the Netherlands.

In separate discussions, the defense ministers were brought up to date on a study of whether older nuclear weapons already deployed in Europe could be scrapped. A U.S. official briefing reporters said no decisions had been made nor a timetable set.