A top official who wanted a "hard shake-up" of foreign aid staff and policy, Frederick T. Van Dyk has resigned as assistant administrator of the Agency for International Development (AID).

Van Dyk, the third-ranking official in AID and a former assistant to Sen. Hubert H. Humphrey (D-Minn.), is the first senior appointee of the Carter administration to resign.

His differences with AID chief John J. Gilligan, Van Dyk said yesterday, were "more pace and style." But he said that added up to a "basic disagreement" with Gilligan, whom he described as a "great friend" who "ought to have somebody who is in more agreement with him."

"My own view of "AID is that we have to shake it up hard, we ought to cut it back," said Van Dyk.

"I thought the place was clearly over-staffed," he said. Many AID staffers "poured back into Washington" at the end of the Vietnam war, Van Dyk said, and "I would think, offhandedly, we could get by in Washington with about half of the people we have here."

"Paperwork," said Van Dyk, "is choking the place."

Gilligan "is moving on it," he said, "but it will be months before anything is felt," and "I would have moved more quickly and drastically."

Van Dyk also headed an interagency task force on all aspects of foreign aid, military and economic. In this study, now nearing completion, Van Dyk said, he favored reducing direct U.S. aid, which meant cutting the role of AID, and placing greater emphasis on aid through international institutions or regional groupings of nations.

This required "a rather ruthless examination" of existing policy, Van Dyk said. Gilligan, he said, will now lead the inter-agency group. AID officials acknowledged there were differences in style and temperament between Van Dyk and Gilligan, but minimized differences on substance.