The Reagan administration, finding itself in the unusual position of having its foreign policy attacked by some conservative intellectuals as inconsistent and too soft, yesterday sent one of its leading intellectuals, arms control chief Eugene V. Rostow, to try to calm his more rebellious colleagues.

Rostow, a former Yale law school dean and professor, warned a gathering here of the Committee for the Free World that conservatives have had previous opportunities, especially during the Nixon years, to alter the course of American and alliance policy and "wasted" them.

"We must not waste this moment," Rostow told a luncheon audience, in an appeal for patience as Reagan's major changes are worked out and in a call for help in solving the problems of carrying out those policies.

"President Reagan has an immense opportunity, and whether he takes full advantage of it is not now clear. There is no doubt about his instincts, preferences and desires. They are as sound as can be," Rostow said.

"But whether we will be able to succeed depends in large part on what intellectuals in and out of government do and say. It has been my experience," Rostow said of his years in government, "that the main overarching problems are intellectual, not ideological. They are not problems of courage or character."

The Reagan administration has recently been attacked by former secretary of state Henry A. Kissinger, who publicly criticized the administration's response to martial law in Poland as too soft and challenged administration plans to begin arms control negotiations with Moscow despite the Polish situation.

Kissinger was the architect of detente with Moscow under President Nixon, and his remarks stung the Reagan White House because they are now being used by some conservatives to attack a president who came to office with strong anti-Soviet views.

Without naming Kissinger, Rostow warned against those "whose primary concern was not a disciplined and rigorous analysis of the situation, but to position themselves within the spectrum of intellectual fashion."

Rostow said, in effect, that while Reagan has set a new course, much has not been thought through, and that intellectuals had a role to play in this process. This "happy band," he said, has above all else a "special responsibility to make sense and with a respect for the evidence."

There has been, for example, a massive increase in the defense budget, which was necessary to stem the tide of 10 years of decay, he said. "But there is as yet no consensus whatever here or abroad about how this new military power should be used," he said.

"We also lack in the U.S. government," Rostow added, "any form of strategic planning. We've always been afraid of it," he said, preferring instead "pragmatism and tactics." Yet, he said, "that lack in our government machinery is fundamental because we can't steer and keep the new course" of the Reagan policy without it.

On Poland, Rostow said the administration "so far has moved very tentatively. Many people have criticized us for not having done enough. But the policy is in a state of evolution, and I suggest you withhold final judgment," he said.

Rostow said "we are only at the beginning of the drama of Poland" and that caution and a combination of carrots and sticks is needed, along with a route that would allow the Soviets to retreat if they could be encouraged to do so.

Attending the three-day meeting here was a large group of generally conservative, though not extreme right-wing, intellectuals from the United States and several West European countries.

Much of yesterday's opening session dealt with what is billed as "the Trans-Atlantic Crisis," specifically the growth of the neutralist-pacificist trend in Europe and what that meant for the future of the Atlantic alliance.

There was a general consensus that these movements are growing and must be understood and countered.

Views on how much of a challenge they present to western unity ranged from that of Rostow, who declined to call it a crisis in comparison to events such as France's pullout from NATO in 1966, to that of Norman Podhoretz, editor of Commentary, who said "what we are seeing in Europe is a pre-emptive decision to surrender to Soviet military power."