Treasury Secretary Donald T. Regan yesterday indicated that the Reagan administration has taken a firm position against increasing the regular lending resources of the International Monetary Fund by more than 50 percent.

He assailed pressure being brought to bear on the International Monetary Fund "to get more money so they can loan out more money" to countries that had already borrowed too much.

In an address to The Washington Post's annual business outlook luncheon, Regan said that some nations have argued that the IMF's resources "be doubled or even trebled" from the current total of about $67 billion. This, he said, "is a game of sophistry and rhetoric in which one calls a modest increase inadequate and tight-fisted."

Regan added, in answer to a question, that an increase of 40 to 50 percent in IMF quotas--the deposits by members that are used by the IMF for loans--coupled with an increase in standby funds advanced by the leading rich nations "will be sufficient to carry us for the next five years from where I see the world economy going."

Regan said in his speech that the Third World debt, which he estimated at more than $500 billion, had been built up by excessive borrowing which must, as is true in this country, be cut back.

"For too many years, the world has been mesmerized by the modern-day money mentality," Regan said. "If spending $10 billion is good, then spending $20 billion must be better.

"And too many nations--including the United States--have bought and bought and bought on a massive scale. And instead of paying, they say, 'Charge it.' So to help make up the shortfall, heavy pressure is now being exacted on the World Bank, the IMF and other institutions to get more money so they can loan out more money."

The Reagan administration is highly sensitive to the likelihood that it will face an uphill fight to get any sizable increase in IMF funding through Congress, even though the U.S. participation in a larger quota does not represent a charge against the budget: Appropriation of U.S. funds for the IMF is offset by a credit on the IMF's books.

Just this week, Sen. William Proxmire (D-Wis.), an influential member of the Banking Committee, warned that increased quotas will be opposed by those members of Congress who view it as a bailout for commercial banks, and by others who see it as foreign aid that might better be kept at home.

Although Regan said some nations had urged doubling or tripling "the lendable resources" of the IMF, he apparently meant to refer to total IMF quotas. Only a portion of the IMF quotas--considerably less than half--is lendable in the sense that they are hard-currency equivalents.

The standby arrangement to which Regan referred is called the General Agreement to Borrow (GAB), which currently can advance about $6 billion through the IMF, but only to members of the lending group. Regan and his fellow finance ministers among the industrial nations have for weeks been working on a proposal to transform the GAB into a larger emergency fund, perhaps up to $20 billion, which also would be available to Third World countries.

The large Western nations that form the GAB have also explored the possibility that the Saudi Arabian government may be willing to put up $4 billion to $5 billion of this total. But whether the Saudis will do so remains to be seen. In recent testimony on Capitol Hill, former Treasury Secretary Henry H. Fowler suggested that to supplement larger quotas and the GAB, the United States should encourage the IMF to borrow in private markets, something the IMF has never done and is not anxious to do.

Further conversations among the major nations on both the IMF quota and proposed GAB increases will take place early next week in Paris. A final decision is scheduled for the IMF's policy-making board, the Interim Committee, in Washington in mid-February.