MONTEREY, CALIF., NOV. 3 -- NATO defense ministers studied details of the proposed U.S.-Soviet nuclear arms treaty today with Defense Secretary Caspar W. Weinberger amid reports he will step down from his Cabinet post.

Dozens of antinuclear protesters marched and chanted outside while NATO's military leaders discussed plans to compensate for the proposed elimination of medium-range nuclear missiles in Europe.

Weinberger, speaking tonight at a news conference, declined to comment on reports of his planned resignation. "All in good time," he said.

However, the defense secretary gave an account of what he considered his major achievements in strengthening NATO. Without the alliance, he said, "we'd have a far more dangerous world and the United States would be far less safe."

Weinberger said Europe will be safer after implementation of the proposed intermediate-range nuclear forces (INF) treaty with the Soviet Union, but said the NATO ministers agreed that a nuclear force will have to remain in Europe as a deterrent to attack by the Soviet Union and that conventional forces will have to be bolstered to offset Soviet superiority.

"I think that the factors that gave rise to NATO about 40 years ago are still there," he said.

Although Weinberger has not announced his resignation, his expected departure was lamented by several allies among the 15-nation Nuclear Planning Group.

"His contributions to NATO's defense are immense," said Col. Winfried Dunkel, spokesman for the West German delegation. "He is very highly respected in our country."

"He is an expert in the field, but he always made it a point not to come to decisions alone," Dunkel said. "He comes to the other NATO ministers to talk about plans instead of telling them the way it must be done."

Most NATO ministers were unfamiliar with Weinberger's expected replacement, national security adviser Frank C. Carlucci, but they foresaw little change in U.S. policy.

One minister, however, Willem F. Van Eekelen of the Netherlands, is a good friend of Carlucci, going back to their days as classmates at Princeton University.

"I think Carlucci has the same ideas as Weinberger," said Van Eekelen's spokesman, Jaap Van der Ploeg. "There won't be any problem for NATO if the change is made, and it will be good for us because our minister is a close personal friend."

Although the NATO nations generally support the tentative U.S.-Soviet agreement to withdraw their medium-range missiles from Europe, including U.S. Tomahawk cruise missiles and Pershing II missiles, there is concern about the timetable of the withdrawal and NATO's vulnerability to Soviet conventional forces.

"We see the possible agreement as very positive, a very good beginning, but we have questions about some details and when it will go into effect," said Erik Senstand, spokesman for the Norwegian delegation.

Weinberger said at the start of the meeting that the United States will maintain its missiles until the treaty is ratified by the Senate, a process with uncertain prospects that is likely to take at least several months beyond the expected signing about Dec. 7 by President Reagan and Soviet leader Mikhail Gorbachev.

The possibility of delaying implementation of the treaty causes concern for some allies, particular the Netherlands, Belgium and other countries where bases are being built for installation of medium-range missiles.

"We want to coordinate in NATO what we have to do after Dec. 7," said Van der Ploeg. "In our country, it seems ridiculous to go ahead with building the base after the agreement is signed by the leaders of the Soviet Union and the United States. It's better to stop then."