There's no mistaking the solid, impassive figure in the easy chair: the white shock of hair, penetrating gaze, measured speech, unflappable air, and pipe, of course. It is undeniably Arthur Burns, economic adviser to presidents and former chairman of the Federal Reserve Board.

But what's he doing, now well past retirement age and with no experience in diplomacy or foreign policy, as American ambassador to West Germany?

Talking sense, as usual. Bringing a fresh eye, a sense of history and a certain ageless understanding to problems in U.S.-German relations and the Atlantic Alliance that are in large part generational. Cutting sharply through conventional wisdom and clich,e analysis. And not being all that delicately diplomatic in dealing with what he perceives to be mutual misperceptions and/or excesses in current attitudes, anxieties and antagonisms.

He has not hesitated to remind the Western Europeans and the West Germans, in a carefully calculated speech some months ago before such talk became fashionable, that Americans pay heavily to maintain 350,000 troops in West Germany, but that the troops "will not stay here if they are not welcome." If the West won't reaffirm its willingness to maintain sufficient deterrence against Soviet aggression, even while negotiating arms control, he warned last December, "there may well be a growing sentiment in America to turn back upon itself" and let Europeans fend for themselves.

Americans, he is frank to say, are too quick to concentrate on "anti-Americanism" in West German protests against U.S. policy. If younger Germans have a sense of alienation, unease and indifference to security demands, they are not alone: "The fading memory of two world wars," says Burns, "has warped the understanding that young Americans have of the links between the security of their country and the security of Europe."

He has no quarrel with those West Germans who don't like U.S. policy and demonstrate against nuclear armaments. But he doesn't at all mind telling those Germans--"young and some not so young"--who equate U.S. and Soviet motives and objectives that this kind of talk "reflects sheer ignorance."

On balance--and Burns is nothing if not balanced--the ambassador comes down somewhere between the doomsday theory that West Germany is sliding inexorably into "neutralism" and the careless insensitivity of the Reagan administration cold warriors whose rocket-rattling preoccupation with a Western nuclear buildup is raw meat to the peace protesters.

Burns has taken pains to meet regularly with groups of young Germans. He finds them "good people," opposed to some U.S. policies, but more troubled by a larger sense of uncertainty about their identity; by a feeling of being at the mercy of the two super-powers; by economic worries for themselves but also a more general caring about economic disequilibrium and inequity, in West Germany, in the Third World.

Add to all this the environmental issue, a distaste for materialism, a distrust of high technocracy and shattered illusions about the United States (Vietnam, Watergate and the first bursts of bellicosity from the new Reagan crowd), and the so-called "peace" movement in West Germany becomes all the more difficult to define.

That it is loud and articulate, and deeply rooted among the young and in the left-wing of Chancellor Helmut Schmidt's Social Democratic Party, is obvious. But as a political challenge to the fundamentals of the alliance relationship, Burns sees it as a "distinct minority."

The polls bear him out. A recent Gallup sampling showed 73 percent of West Germans with a positive or favorable view of the United States, with 77 percent thinking just the opposite of the Soviets.

This is not to suggest that the ferment in West Germany can be lightly dismissed. Though Burns doesn't quite say so, others argue that it can be inflamed by loose American discourse on the nuclear arms issue--and was in the Reagan administration's early days. That it can be sensibly and constructively addressed, most observers here believe, was also demonstrated by the assuaging effect of Ronald Reagan's temperately expressed "zero option" nuclear offer last November.

The president will have every opportunity to improve on that image-building on his visit here in the course of his European passage in June. How effectively he does so may well turn on how much his approach is informed by the unconventional wisdom of Arthur Burns.