The Institute for International Economics yesterday recommended steps for the World Bank and International Monetary Fund to take to "consolidate and strengthen" their efforts to deal with the longer-run aspects of the Third World debt problem.

The Washington-based think tank urged the two lending institutions to take a series of steps at their meetings here next month that would allow them to take advantage of the current period of relative calm that has followed the eruption of the 1982 debt crisis.

Coincidentally, another private, nonprofit organization -- this one of 200 commercial banks that claim to represent more than 80 percent of the commerical loans to Third World countries -- addressed a separate letter to the World Bank and the IMF warning that banks can not be expected to keep up the lending pace of the late 1970s.

The banks feel "that international organizations should provide more financing," Andre De Lattre, managing director of the Institute for International Finance Inc., wrote the two institutions.

De Lattre said that the banks welcome the adjustment efforts made by borrowing countries, and urged the two international organizations to "encourage foreign direct investment, domestic savings and return of flight capital."

The IMF's policy-making board, the Interim Committee, will meet here on April 18. Then, on April 19, there will be a meeting of the Development Committee, which is jointly sponsored by the IMF and World Bank.

The steps recommended by the Institute for International Economics were drafted by that agency's economists, C. Fred Bergsten, William R. Cline and John Williamson. The authors analyzed 24 possible types of change in the terms of bank lending to developing countries, and in related policies of the recipient countries.

They conceded that none of the steps they recommended, taken alone, would make enormous changes in the outlook for easing the debt problem. But the three authors said it would be a mistake "to sit back and simply bask in the progress to date."

After sifting through the 24 possible policy options, they recommended that the IMF and World Bank pursue:

* "Mexico-type" packages, designed to reduce bank fees and spreads, along with longer maturities, as successfully negotiated with Mexico and Venezuela last year.

* Use of interest rate caps, with deferral of interest above the caps, in extension of new bank loans, the idea being to limit the impact of any future sharp jumps in interest rates.

* Creation within the IMF of a fund to subsidize interest-rate fluctuations on IMF loans.

* Increased loan insurance by government and private insurance agencies.

* Broader use of the World Bank's guarantee authority to encourage expanded private credits "to countries pursuing responsible policies."