The NATO defense ministers today reaffirmed their commitment to deploy the first U.S. medium-range nuclear missiles in western Europe during the next two months.

They also gave a cool reception to the latest Soviet arms control proposal designed to head off deployment of the Pershing II and cruise missiles.

Confidence that political opposition is on the wane and that deployment will begin as planned dominated their two-day session here, making it almost certain that the superpower game of nuclear "chicken" will start in December.

Defense Secretary Caspar W. Weinberger reflected the overall sentiments here, saying the discussions on deployment were "the most harmonious" he had attended.

In fact, the only hint of controversy at the meeting, sources said, emerged today in talks about whether any positive tone would be used in rejecting the most recent arms control proposal by Soviet President Yuri V. Andropov.

On Wednesday, the Soviet leader said his country would be willing to cut its number of SS20 missiles in eastern Europe to 140, from the 351 that U.S. sources say the Soviets have there.

The new offer lowered by about 22 missiles an earlier proposed figure, but Andropov again tied such a reduction to the United States forgoing any medium-range missile deployment.

In their final communique, the NATO ministers said they did not "welcome" the Andropov proposal as they had in mentioning a U.S. initiative in the missile talks.

Instead, the ministers "noted with attention" the Soviet proposal and "invited" the Soviets "to explain fully their proposal at the negotiating table."

As if to show that they know the Soviets were not serious, the ministers quickly added that the "Soviet Union regrettably continues to insist on a monopoly in land-based medium-range missiles."

The final communique also took issue with Andropov's threat to end Soviet participation in the Geneva arms control talks on medium-range missiles.

First, the ministers noted that "the West has continued to negotiate for years while the Soviet SS20 buildup has continued."

Thus, the communique argued, "the Soviets therefore have absolutely no justification for breaking off negotiations as NATO's deployment goes forward."

During the closing news conference, British Defense Minister Michael Haseltine said there is no need to delay deployment, as the Soviets are demanding. "Two months is enough time," he said, for the Soviets to come forward with a real arms control proposal, adding that there is "no indication they want to do so."

Haseltine said the Soviets have used the four years since NATO decided on deployment "to build up their own missiles and to seek to create opposition" to the U.S. missiles.

"They have singly failed to do the latter," he said.