A general sense of unease over the world's financial crisis pervaded the atmosphere here on the eve of the formal opening of the World Bank-International Monetary Fund sessions.

Bankers, in private conversations, traded the latest in rumors that Brazil or Argentina or other countries might have to join Mexico in rescheduling their foreign debt.

A U.S. official commented that, "The IMF probably is having talks right here in this Sheraton Centre hotel" with one or more countries in an effort to prepare for any future crises.

Although there was nothing specific to substantiate such rumors -- and officials from Brazil and Argentina consistently denied them -- the fact that the policy-making Interim Committee had taken no step to shore up the international monetary system added to the worries. The big rise in the price of gold in the world market to about $457 an ounce last Friday was seen as a symbol of the uneasy state of financial markets.

In the face of that unease, a senior U.S. official attending the meetings repeated today that proposals for a "substantial increase" in IMF resources is not warranted and has not been justified by its proponents.

The Interim Committee said in a communique Saturday that there was "widespread approval" for a "substantial increase" by virtually all members except the United States.

But the American official told reporters that, "Until I can find out what they the IMF want to use it for, I'm not going to agree to anything."

He was especially scornful of a proposal -- backed by some in the IMF and by the poor nations -- to double the IMF "quotas." Quotas are deposits of currencies by member countries that are used for loans.

The United States has approved only a small and as yet undefined increase in quotas. The senior American official here said that to double them would give the IMF "over $100 billion" to finance balance-of-payment deficits. "What are they going to do with it?" he said rhetorically. "We did not have that much of a global deficit in the first oil crisis or in 1979."

Currently the IMF quotas total about $67 billion. Proposals for an increase, which would cover a three-year period beginning in 1985, range from a European suggestion that they be boosted at least 50 percent to the 100 percent suggestion offered by recipient countries and by the IMF staff.

Meanwhile, the American delegation contends that Treasury Secretary Donald T. Regan's tentative suggestion of a "crisis fund" to supplement IMF quotas is still alive.

Although the Interim Committee did not approve the idea on Saturday -- referring it instead to the executive board for further study--the senior official insisted that "as we explain it to them, we are able to disarm some of their suspicion."

The suspicion he referred to relates to the possibility that the proposal would divert attention from the need for a permanent increase in IMF funding, or that it might pass power over disposition of large funds from the IMF to a smaller group of nations advancing the money for the crisis fund.

One convert to the U.S. proposal, according to the American official, is Jacques deLarosiere, the IMF's managing director. The American official said that deLarosiere "now sees it as an opportunity to enhance the fund. In fact, he told me that, 'Anyone in the IMF who spits on the idea should be fired.' "

DeLarosiere did express support for the crisis fund, in the words as quoted, when he was assured that the proposal was to supplement IMF quotas and that any such fund would be administered by the IMF.

But IMF sources reiterated that a "fear" persists among many nations that such a new scheme would acquire a life of its own outside of the fund. One such official said, "There is no concrete proposal, in any event. We ought to see it before we decide."

Those familiar with deLarosiere's views say that he has concluded that the IMF will need U.S. support to get agreement on a quota increase and that if quotas are not boosted by at least 50 percent, additional funds from some source will be needed.

But the suspicion prevalent in the American delegation on getting the fund a major boost of resources was clear in a paper used by Regan Saturday at the Interim Committee meeting, which said that there has been "an enormous expansion of individual countries' potential access to IMF resources, far in excess of historical norms" and "strains on the fund's financial structure."

As the senior American official told reporters, "We think a lot of these guys are confusing the IMF with IDA International Development Association . The IMF is not an aid agency." The IDA is the World Bank's concessional loan agency.

Meanwhile, the Development Committee, a joint operation of the IMF and World Bank, issued a communique welcoming the agreement by 22 donor countries to release the remainder of their contributions to the IDA. These contributions are for the current IDA program, known as IDA-6, the current replenishment of IDA funds.

Under the original IDA terms, all donor countries were entitled to reduce their contributions on a pro rata basis with the United States, which had cut its contributions by about 35 percent. The willingness of the other nations to put in their full contributions, the Development Committee said, will help to keep IDA at least partially effective for the next year.