International Monetary Fund Managing Director H. J. Wittveen surprised the international financial community yesterday by announcing that he will leave his influential post next August.

Witteveen, who in the normal course of affairs would have begun a second five-year term Sept. 1, 1978, withdrew "for personal reasons."

Sources close to the IMF managing director said he had decided not to stay away any longer from his native Holland, where his wife and four children are living. The serious illness of a teen-age child is an associated reason, friends in the IMF said.

A one-paragraph IMF announcement said Witteveen had told the executive directors "he does not wish to make himself available for a seconod term in this position."

Witteveen, 56, had been an innovative manager at the IMF, playing a large role in the amendment of the articles of agreement which will give the agency more influence in monitoring the international monetary system.

He also engineered two special lending facilities in the wake of the 1973 oil crisis to help poor nations meet their balance of payments deficits. The second of these special funds, just taking shape, already has been dubbed the Witteveen Facility in his honor.

Under Secretary of the Treasury Anthony Solomon yesterday expressed regret at Witteveen's planned departure, noting that it had come suddenly and represented no policy disputes.

At a briefing on U.S. views on matters to come up at the annual meetings, Solomon and Assistant Treasury Secretary C. Fred Bergsten said they "do not look for many fireworks" or initatives.

Solomon said that no firm decision would be reached by the Interim Committee on the size of the next, or the 7th, quota increase for the IMF, nor had the U.S. decided on how large an increase it is prepared to support.

But he added that the U.S. prefers an increase "that does not involve any change in (relative) shares," although it is "prepared" to listen to arguments "for a very few selective increases."

Similarly, although the U.S. agrees in principal that the World Bank needs a general capital increase - a turnabout from the Ford administration view - no hard numbers have been settled.

Solomon said that there would be an intensive discussion at the Interim Committee meeting on the world economic outlook. He said the U.S. looks for only "a modest improvement" in 1978 over the anticipated Organization for Economic Cooperation and Development growth rate "somewhat under 4 per cent."

He added that "our over-all expectation at this point is for no major surge in recovery - this is not a recession, but it certainly does not make any significant dent in the unemployment totals." There is no need, how ever he said, for a "drastic revision" of the international economic strategy laid down at the 1976 annual meetings at Manila, or at the London economic summit last May. But he said the Interim Committee would ask countries like Germany that missed their growth target to explain why.

In answer to a question, Solomon stressed that he did not challenge the good faith of the West German government (which set a growth goal of 4.5 to 5.0 per cent, and appears to be hitting something less than 4 per cent for this year). But he said that, "in hindsight, the (stimulus) package now going forward (in Germany) would have been useful earlier in the year."

Choosing a successor to Witteveen will now be an unofficial topic of discussion at the annual joint meeting of the IMF and World bank group and related sessions that begin in Washington over the coming weekend. By custom, the IMF managing director has been a European, while the World Bank presidency goes to an American.

Speculation yesterday included the name of Willy de Clerq, a Belgian who has been chairman of the IMF's policy-making Interim Committee. Because his political party was not included in the ruling Belgian coalition after an election last April. de Clerq is expected to resign, and be replaced when the Interim Committee meets here this Saturday just prior to the annual meeting.

Other possibilities for the Witteveen job include the British Chancellor of the Exchequer, Denis Healey, and the Secretary General of the OECD, Emil Van Lennep. Lennep was in the running for the post when Witteveen was selected by the executive directors in 1973.