A major expansion of the lending resources of the International Monetary Fund has been agreed upon by the United States and other principal contributors in an effort to grapple with a growing financial crisis among Third World debtor countries.

Complicated, world-wide negotiations are still to be concluded, but it is likely that the IMF will get an infusion of almost $30 billion in additional hard, "usable" currencies for loans to needy countries. Some of the funds may be doled out earlier than planned.

The new monies to be pumped into the IMF would consist of a 40 to 50 percent increase in IMF quotas -- deposits by the member countries -- and a new or expanded special lending facility to which the major rich nations would make additional contributions.

In an interview, Treasury Undersecretary for Monetary Affairs Beryl Sprinkel said, "We hope we can start the new quotas earlier than 1985 as presently scheduled , and the sooner the better." Given the need to get legislative or parliamentary approval, this may prove difficult, he conceded. But he indicated that the new quotas could come into being in 1984.

West German IMF Governor Karl Otto Poehl, here for discussions with American officials on these questions, said in a separate interview that it was less important to advance the effective date of new quotas than to get an early agreement, which would encourage commercial banks to lend, rather than hold back as they have been.

Fears that IMF funds would be exhausted, leading to a collapse of the international financial system -- including defaults on developing country debt that might as a consequence bankrupt some major banks -- have added to a sense of urgency.

Sprinkel said there needs to be and will be "a major increase in IMF funds. The IMF has to be the major actor in this critical situation, not the only one, but it must play the starring role."

Moreover, as a symbol of the urgency with which the Reagan administration now views the problem, Sprinkel revealed that the United States has recommended advancing -- possibly to February 1983 -- the date of the Interim Committee meeting, now scheduled for late April, when the IMF funding question is supposed to be settled.

IMF sources estimate that, counting regular and special funds, it has available less than $20 billion of "usable" money for loans and that this pot is rapidly dwindling in the face of emergency needs in Mexico, Argentina, Brazil and elsewhere.

Poehl, who met Friday with Treasury Secretary Donald T. Regan, U.S. governor for the IMF, said that "things may yet get worse before they get better -- we face a 'winter of discontent' such as we have not experienced for quite some time."

In a Boston speech last Tuesday, Federal Reserve Board Chairman Paul A. Volcker also took a grim view of the situation and said that the negotiations over enlarged IMF resources "should, and can, be brought to an early conclusion."

Present IMF quotas, scheduled to last through 1985, now total 61 billion Special Drawing Rights (SDRs), worth approximately $65 billion. It now seems likely that new quotas will be boosted to as much as 90 billion SDRs ($95 billion) and, as Sprinkel said, may be made effective earlier. A portion of the enlarged quotas, all of which come from the member nations' local currencies, is not useful as loans to others.

Although the position of the United States is much more forthcoming than it was at the Toronto meeting of the IMF and World Bank last September, it says that if the quotas are increased, the IMF must consider whether each country's access to borrowings may prove to be too liberal.

The Reagan administration also has warned the other nations that it may have a delicate problem of shepherding the proposals through Congress, which is overwhelmed with the problem of a massive federal budget deficit and doesn't like what it calls "foreign aid" -- even if others consider contributions to the international lending organization neither foreign aid nor a drain on the budget.

To maintain its conservative posture, the Treasury has raised the question within the IMF whether the agency's present rule allowing each country to borrow a maximum of 450 percent of its quota should be trimmed back, if quotas themselves are to be boosted. The poor countries argue, in effect, that this would be taking back with one hand what is given with the other.

To handle the more immediate borrowing needs, there is also agreement that, in addition to larger quotas, there will be a separate, special fund -- perhaps about $20 billion -- to be administered separately by the IMF.

A debate as to whether this should be a new fund, as originally proposed by the United States at Toronto, or an enlargement of the so-called General Agreements to Borrow (GAB) is still going on.

Poehl said that the German government favors boosting the GAB, now holding about $6.5 billion in funds, enlarging it and making it available to developing nations on a selective basis. Currently, only the Group of Ten contributing nations can use the GAB money.

Sprinkel said that the United States is also swinging around to the GAB concept, assuming that it can be modified to bring in other lenders, such as Saudi Arabia.

If quotas are increased by the equivalent of around 30 billion SDR, roughly half would be in lendable or "usable" currencies -- say, around $16 billion. If the GAB is increased to $20 billion from $6.5 billion (all usable currencies), that would add another $13.5 billion, for a rough "usable" infusion of about $30 billion for the IMF.

"It's not really enough," international economist C. Fred Bergsten commented, "but I suppose it's a reasonable compromise between the real world and what you can do. It will last for a few years, and then they'll have to come back for more. Historically, every IMF quota increase has been less than what they've needed."

After the meeting Friday between Regan and Poehl, Sprinkel said that "although there is not full agreement, I am confident that there will be a meeting of the minds among major nations.

"We will demonstrate to the world that we are cognizant of our responsibilities to provide adequate funds to the IMF during this period of troubled credit conditions."

Poehl echoed essentially the same note: "The IMF is the only hope. The IMF is the only institution that can lend money and put conditions on it. No government can do it; no bank can do it."

Once the IMF has enlarged resources, Poehl said, banks will come back into the lending picture. "You can't do this rescue operation without the commercial banks. If one bank after another wants to step out, we're in trouble. Therefore, the problem is how to assure the banks it's reasonable for them to stay in," Poehl said.

West Germany, like many other European countries, favors at least a 50 percent increase in new IMF quotas. Sprinkel would not reveal the precise U.S. position, but American negotiators reportedly have moved up their offer to a 40 percent increase. This is an major shift in the U.S. position. Initially, the United States was reluctant to expand the IMF quotas at all, while IMF Director Jacques de Larosiere this past summer was urging an increase of up to 100 percent.

At Toronto, the United States proposed a token quota increase of 15 percent (around $10 billion), plus a brand-new emergency fund that could be used in the interim period before the new quotas became effective. No dollar figure was ever officially put on that fund.

But the Third World countries and most of the major European nations pressed for the more permanent expansion of lending authority that would come from larger quotas. And the IMF policymakers directed that both ways of adding to the IMF's stature be studied and resolved no later than next April.

IMF officials are happy that, as Poehl says, a major expansion of their fund and its role seems to be "on track." But they are doubtful that the negotiations among all the governments can be pulled together before April.

First, there is the question the United States has raised on whether to cut back the borrowing access below 450 percent, which is angrily resisted by the Third World countries. Then there is the question of whether the "emergency" fund should be temporary or permanent.

The IMF is not anxious to have the emergency fund permanent. It would rather weight the package in favor of the quotas, so that it would not be dependent, as one official put it, "on the sufferance of one or two countries such as Saudi Arabia."