United Nations, N.Y.
An iron fist in a velvet glove.
This is how many diplomats here describe Javier Perez de Cuellar, the Peruvian who is the new secretary-general of the United Nations.
In his first interview with a reporter, given Thursday, Mr. Perez de Cuellar disclosed that he plans to:
* Put the UN house in order by making its machinery cost-efficient, lean but productive, and hard-driven.
* Speak out forcefully and act tenaciously behind the scenes to try to defuse the present East-West and North-South tensions.
He also wants to ''give the UN a new sense of self-esteem, of direction, and thus to lend it a new thrust as the protector of civilized behavior in the jungle of international affairs.''
Indeed the new secretary-general, who has been in office one week, is carrying out a major shake-up in the higher echelons of the organization.
An audacious change he is expected to make this week is replacement of the director general for development and international economic cooperation, Ghana's Kenneth Dadzie, with France's progressive-minded but pragmatic Jean Ripert. The change in that position - the second-highest at the UN - and other personnel shifts are deemed essential by Perez de Cuellar to restore the UN's credibility and to help it ''to be taken seriously.''
''Cautious and bold. Independent and realistic. Quiet but firm.'' This is how he sees himself in the role of secretary-general, as he told the Monitor.
In appointing Jean Ripert, the new secretary-general is understood to want to erase the impression that has been created in the West that the entire UN system has become captive of the developing nations. He himself comes from the developing nation of Peru. The heads of UNESCO, the Food and Agriculture Organization, United Nations Industrial Development Organization, United Nations Council on Trade and Development, and International Fund for Agricultural Development all come from the third world.
If there is to be a meaningful North-South dialogue, the industrial nations must not have the feeling that the deck is stacked against them at the bargaining table.
As a member of the staff of Jean Monnet (the Common Market's founder) in the '50s, and as a former French high commissioner for economic planning, Mr. Ripert has credentials to speak for the industrial nations.