The World Bank must play "an expanded role" and be "a bit more aggressive in its lending" to help meet the Third World debt crisis, according to Bank President A. W. Clausen. But American reluctance to commit the necessary resources for expansion of World Bank activities, he adds, is a constraining factor.

Clausen said in an interview that allowing a modest expansion of bank loans "is the least costly way for the rich nation owners of the bank to help the debt-ridden countries put projects into place" that would boost their export earnings, creating a critical cash supplement to the emergency loans such nations are getting from the International Monetary Fund.

The former BankAmerica chief flatly ruled out any of the variously proposed debt-consolidation schemes under which the bank or some other institution would take over and stretch out the unpayable debts of the less developed countries. Buying up distressed loans and writing bonds against them "is not our business--our business is development," Clausen said.

"I am no more interested in a debt-consolidation proposal made by New York banker Felix Rohatyn than I would be in trying to manufacture a pill that will cure all ailments in individuals. Because you hurt in the ear, and I hurt in the toe, and the next guy hurts in the stomach, and so for each one, we need to give custom treatment."

To boost its lending significantly, the bank must borrow more money--which it can do easily with its high credit rating--or expand its capital resources. But expanding the bank's activities is meeting resistance in some governments, notably in the United States.

For the time being, as a matter of strategy, Clausen is content to de-emphasize the bank's intention to seek additional capital, fearing that he would be "overloading the circuits" while the IMF appropriation bill--which Clausen labels "the No. 1 financial priority on planet Earth"--is still before Congress.

Meanwhile, the bank has already "accelerated" some of its lending through what it calls a "special action program," pumping about $2 billion over three years this way into projects. It also is putting about $1 billion a year, or 10 percent of its total loan kitty, into "structural adjustment loans," which are less like the typical World Bank project loan, and more like the shorter-term IMF advance.

Yet, at a time of dire need among the ranks of Clausen's Third World customers, many observers have complained that the World Bank is not doing enough, or quickly enough. That there is at least some validity to this complaint was publicly acknowledged by Bank Vice President Munir Benjenk, who pointed out during a recent World Bank seminar at Columbia, Md., that the failure to use the bank more "is quite incomprehensible and somewhat absurd."

Benjenk noted that commercial banks and other lenders who are "leery" of making new commitments to Third World countries--because of the mounting debt problem--are anxious to place their funds in World Bank bonds.

"We can borrow more, and therefore let us lend more in the present situation . . . and let us do this so that the adjustment which is necessary in the developing countries can be gradual and not brutal," Benjenk said.

Clausen revealed in the interview that because of the debt crisis, many country clients of the World Bank have had to abandon development projects that would have stimulated economic growth and added to their ability to export goods.

For example, he reported that "the Philippines is scrubbing 11 development projects, or $5 billion. Indonesia is reducing . . . $35 billion in development projects over the next decade. And so on--country after country."

Once Congress has approved $8.4 billion in new funding for the IMF, the bank will be pressing its member countries to approve, first, a $20 billion "selective" capital increase, and later on, a $40 billion "general" capital increase. This was given the green light at a Washington meeting of the Development Committee, a joint World Bank-IMF board, in late April.

The selective increase will be requested in two stages designed to ease the burden on major country budgets--a first installment of $3 billion, with the balance of $17 billion deferred until 1986, when the bank also will be seeking its general capital increase.

Capital increases for the multilateral lending agencies are largely "callable" funds--tapped when necessary, with only very small amounts (typically 7.5 percent or less) actually appropriated and "paid in" to the banks.

But things are moving more slowly than had been hoped by bank officials at the time of their seminar at Columbia in May. Because of national deficits and other troubles with their home economies, the heads of government were less forthcoming at the Williamsburg economic summit than they were a year earlier at Versailles in promising help to the multilateral development banks such as the World Bank.

This was a bitter disappointment for the World Bank and Clausen, who had lobbied strenuously before the Williamsburg summit with a number of European leaders who--they thought--had promised to push hard for a commitment to more development aid in their conversations with President Reagan.

A European draft of the Williamsburg declaration proposed to say that the leaders were "greatly concerned" about the debt crisis, but the final document scrapped the word "greatly." There was also a draft reference, finally deleted, which spoke of "agreement of the importance of replenishment of aid funds for the future."

At Versailles in 1982, the leaders had endorsed a continuation of subsidized World Bank lending through the International Development Association, specifically urging "an early start to consideration of IDA-7 replenishment funding ." At Williamsburg, with IDA-6 still not funded, there was no mention of IDA-7, merely a promise to provide "agreed" funding levels, meaning IDA-6. Yet, Clausen said in the interview that IDA is still the bank's "highest priority."

IDA, the bank's soft-loan affiliate, makes long-term, interest-free loans with only a small service fee to the poorest of the bank member nations. But the United States has fallen behind in its actual appropriations of concessional money for IDA-6, stretching out what had been a three-year program to at least four years. Whether it must stretch to five years depends on congressional action in the next few weeks.

In a candid discussion of the bank's current problems, Clausen said that he believes that the primary service the bank can render in the present crisis, supplementing the major role of the IMF, is to help poor nations expand their export potential with medium term, 15- to 20-year loans.

"The fundamental philosophy of our institution is to help countries diversify their exports, we believe, and to have an export orientation . . . It's one's ability to earn foreign exchange that will make an economy more efficient," Clausen said.

An example of the kind of "special action" the bank can take was approval June 24 of $525 million in loans to Mexico to assist export development, and to promote small- and medium-scale industry. This was followed by a package of $519 million in similar loans for Turkey.

Although these loans fit Clausen's criterion of stimulating long-term development, rather than duplicating IMF balance-of-payments assistance, they are also geared to activities that might quickly affect the economies of the two countries.

Some critics suggest that in the present crisis, the bank needs to do more of this kind of lending, consciously shifting its focus away from IDA and concessional programs.

For example, in testimony before the Senate Foreign Relation Committee earlier this year, economist Rimmer de Vries of the Morgan Guaranty Trust Co. said that the World Bank had been too optimistic about the export prospects of developing countries, anticipating higher economic growth and lower interest rates than had developed.

Because actual experience has been "painfully different," de Vries predicted that "it may be years" before some of these countries have access to the international capital markets. He concluded: "Ensuring that they get the long-term funds needed for economic development may require the World Bank to rethink its lending priorities."

But so far as Clausen is concerned, he said in the interview, IDA still has the No. 1 priority. The last negotiated aid package for IDA--for IDA-6--was $12 billion. At a meeting of IDA deputies July 19-21 in Tokyo, the bank staff will propose a $16 billion program for IDA-7, which just barely would keep IDA level in real terms.

But since China would now be an IDA recipient, entitled because of its population and per capita income status to a large share of whatever total IDA funds are put together, every other recipient will take a large percentage reduction.