CARL KAYSEN is a professor-turned-administrator. After a two-year stint advising the Government on foreign affairs, he returned to Harvard in 1963, prepared to spend the rest of his career here, teaching and doing research in political economy. But in 1966, when trustees of the Institute for Advanced Study in Princeton approached him, asking him to take over J. Robert Oppen-heimer's post as director of the "intellectual hotel," he could not resist their offer.

Kaysen is eager to take full advantage of the place that made Albert Einstein exclaim, "Ah, Heaven!" when he first arrived. But times have changed since Einstein's day, and Kaysen has had to spend much of his time raising money to support the Institute's roughly 200 permanent and visiting members.

Kaysen is definitely not the fund-raising, nine-to-five type, but he thinks the adventure is worth it: a community of scholars free to think without the pressures of classes and graduate students and the publish-or-perish syndrome. Much of his administrative work is dull, but Kaysen is willing to endure it for a chance to transform some of his ideas into reality.

He plans to make his first departure from Institute tradition this fall: he will add a small School of Social Sciences to the Institute's long-established Schools of Historical Studies, Mathematics, and Natural Sciences. Kaysen envisions the new school not only as bait for good economists and other analytical social scientists, but as an addition to the field. "It would make no sense just to add a school of economics," he explains. "Harvard or Yale or Berkeley could do just as well or even better. But right now, no one is thinking about history from the social sciences point of view--from a more analytical standpoint."

Kaysen hopes to do some more analysis of his own after he has settled in at the Institute, but so far his time has been taken up with administrative duties, he says with a wry grin. In spite of his preoccupation with the Institute, Kaysen still finds time to attend meetings of the Advisory Committee for Economic Development, which advises the Agency for International Development, and for such public services as delivering the Oliver Wendell Holmes Lectures at the Law School here last week. "Cambridge still feels like home," Kaysen remarked last week during his two-day stay, but at just-48, he has lots of time to get used to Princeton. And he is excited about launching his new school: "I expect it to make a contribution to the way the subject develops. We'll begin with an idea and a few scholars, and see what happens--just the way the Institute began."

BUT Kaysen is less willing to talk about affairs in the Big World outside the Institute's green fields. There one must be careful of the Government, of one's reputation--and Kaysen sticks to his position as an economist. From an economic standpoint, he says, the country can easily support the war. Although to do so, he amends, it must "take a lot of resources which could much better be used on other things. The situation looks in a very critical shape."

Kaysen does not feel that the war-protestors are accomplishing much by civil dsiobedience, but, he admits, "On the whole I'm in sympathy with them. Still, I guess I'm over thirty"