Washington — A President beset by problems is moving to the offensive. That, administration insiders say, is an underlying motivation behind President Reagan's ''historic'' missile-reduction proposal.
By moving to ease tensions with the Soviet Union, Mr. Reagan may, as some critics here already are saying, be asking for concessions that Soviet President Leonid I. Brezhnev will never accept. But they concede that Reagan's offer might open a path toward reducing the danger of nuclear war.
Reagan's proposal is regarded by observers here as one that may remove some of the President's swashbuckling, hawkish image in the eyes of many Americans and many people in the rest of the world.
Reagan's top diplomatic and military advisers assert, as Secretary of Defense Caspar W. Weinberger did over breakfast with a group of reporters Nov. 18, that the President's proposal ''was not propaganda in any way. . . . It was a very serious proposal aimed at securing lasting peace. . . . And we think it will succeed.''
But behind the scenes Reagan aides admit they hope that one very important aspect of this initiative will be to reduce anxieties in Western Europe about the President and his attitudes toward possible nuclear exchanges centered in that region.
At one point Mr. Weinberger said that the proposal ''was not to quiet the demonstrations'' in Western Europe. But at another point he indicated that ''there was consideration'' given to the uneasiness there.
Additionally, the President's ''peace offensive,'' as the White House is calling it, tends to divert Washington and public attention away from the President's still-boiling problems with his key aides.
The credibility of Budget Director David A. Stockman, and national security adviser Richard V. Allen and the $1,000 ''thank you'' money, are still in the spotlight here - but less so now as the media focuses on the President's foreign policy.
The administration takes the position that the proposal was, as Weinberger says, a ''single, clean, and tremendously important'' effort toward easing global tensions. And the administration rejects the suggestion that the timing of the proposal was tied in with any kind of propaganda objective. Weinberger says that the proposal was being put together ''quite a long time ago.''
Yet, a top administration aide indicated a few days ago that something was in the making that would tend to help Reagan in his effort to regain his momentum. And another administration source has disclosed that this speech was part of the President's new offensive.
It seems clear that the President's speech signaled his decision to involve himself more in foreign affairs. Undersecretary of State James Buckley told reporters Nov 17 that this speech would be followed by other presidential utterances outlining his policy in other areas of the world.
Thus, Reagan is seeking to regain his pace once again by concentrating more on foreign affairs. Observers here note that other presidents have followed the same route.