The United States will reject as "unnecessary" a proposal to double the lending resources of the International Monetary Fund that will be made over the weekend in Toronto just prior to the IMF's annual joint meeting with the World Bank, Treasury Secretary Donald T. Regan said yesterday.

"We're not anywhere near that," Regan told a press conference. Although there is support for a large increase among major U.S. European allies, in the IMF bureaucracy, and among the poor nations, Regan said such a move held a danger "of all this new liquidity sloshing around."

Therefore, the United States will support only "a modest increase" in IMF "quotas" -- the amount of currencies that are placed on deposit by IMF member countries and that form the basis of IMF loans to countries in trouble, he said. These quotas now total about $67 billion.

Regan said that the United States will suggest an alternative to a major quota increase for the IMF. It will propose to other major nations, which now provide standby borrowing authority to the IMF through the General Agreements to Borrow (GAB), that these credits be expanded and made available to poor countries in an emergency.

The quota proposal will be brought up Saturday at the Interim Committee of the IMF, and separately at the Group of Ten industrial nations. Regan may broach the subject of enlarging the GAB resources at a dinner with the finance ministers of West Germany, Japan, France, and Great Britain -- the Group of Five -- before the G-10 and Interim Committee sessions. The annual meeting itself begins on Monday.

Regan acknowledged that "there will be a lot of pessimism about the world economic situation and concern about the international economic situation" in Toronto, and that "there is danger" in the international banking system that will persist so long as problems such as those in Mexico, Poland and elsewhere persist.

He said he had no way of analyzing the impact of Mexican President Lopez Portillo's nationalization of Mexico's banks (which was being announced as his press conference was being held).

Regan argued that the negative factors "need to be balanced by a realistic appraisal of some of the positive things" now happening in the world economy. He predicted that, after two years of almost no economic growth, the industrial nations will rack up a gain of 3 to 4 percent next year.

This is considerably more optimistic than projections by the IMF or the Organization for Economic Cooperation and Development in Paris.

He stressed that there will be no decision at the Toronto meeting on the question of IMF resources. The quota review process must be completed by late 1983, "and we think that is a realistic schedule," Regan said. But given the pressures generated by the Mexican debt problem, other nations likely will be pushing the United States for speedier decisions to prop up the creaky international financial network.

Under the present rules, the GAB credits -- now equal to about $6 billion -- are available only to the small network of rich industrial nations contributing the money. The U.S. proposal, first outlined in vague terms in a letter by Treasury Undersecretary Beryl Sprinkel to other deputy finance ministers, still is highly tentative. It would broaden eligibility for the GAB credits on short notice in emergencies, supplementing IMF quotas.

Regan said he had no knowledge of a reported $25 billion emergency fund to be used in a global crisis. "I don't know where that figure came from," he said. We "never surfaced such a figure." Federal Reserve Board officials said that a $25 billion figure was used by a junior staff member, but never had been considered by the board.

IMF officials, who also said they had no knowledge of anything like a $25 billion pool of money, suggested that the entire American initiative was designed to deflect attention from the need for a large quota increase.

On World Bank matters, Regan said that he would be "reasserting our commitment to the important role of the multilateral development banks in the development process." But as in the case of the IMF, the United States will be a holdout against the desire of other major nations to be more generous in funds for the International Development Agency, the soft-loan affiliate.

The United States has stretched out to four years a $3.24 billion commitment to the IDA that was supposed to cover only three years, causing a shortfall in the entire program. As they are entitled to do, many nations have sliced their contributions in pro rata fashion.

"Our concern is that, in light of domestic belt-tightening, the international lending institutions should be subjected to the same kind of scrutiny," Regan said.