No one here likes to talk about it, but the International Monetary Fund--lender of last resort to Third World countries unable to pay their bills--will have to be less generous in handing out the money next year. This will be the case even if Congress in the next few days reluctantly approves an $8.5 billion appropriation for the IMF as the U.S. share in increased capitalization for the agency.

What impact an even tighter-fisted IMF could have on the world debt crisis can't be predicted. World economic recovery--especially if interest rates decline further--could ease the pressures smewhat. But global recovery is far from assured, and indications point to a rise in American interest rates, which would be bad medicine for all debtors.

Last year, those Third World countries had to slash their imports by $42 billion, according to the IMF. With commercial banks reducing their Third World exposure, lack of sufficient IMF funds could force further curtailments of economic activity that would be felt immediately here and in other industrial countries.

IMF Managing Director Jacques de Larosiere has been running all over the world trying to scrounge an additional $2 billion to $3 billion in loans from Western Europe and Japan. This would help tide over a shortfall in money the IMF had anticipated--prior to the oil price decline--that it would be able to get this year from Saudi Arabia.

De Larosiere may come up empty-handed, in which case he will have to report to the IMF annual meeting in Washington this fall that the organization's ability to help the hard-pressed Third World countries has been reduced.

De Larosiere provided a hint last week of how touchy the situation could get, noting that the fund had entered into existing loan commitments running close to $27 billion, with additional requests piling up.

"The fund's liquidity position (therefore) is under considerable strain," the IMF offcial said. It was learned that De Larosiere's kitty of lendable funds may be some $2.5 billion short at the end of the year, unless he can replace the Saudi shortfall with money from major countries--or, possibly, by tapping the commercial market.

Even though supporting the IMF as the centerpiece of the international rescue effort, American and German officials think that the IMF must put an absolute limit on the total drawings any country can make, once the IMF's basic capitalization is increased 48 percent, or $32 billion, to the equivalent of $96 billion.

As it is now, the IMF allows a member country, if it meets certain conditions, to borrow up to 450 percent of its own quota (its own currency deposits in the fund) over a three-year period, and 100 percent of its quota in unconditional money for certain emergency needs.

Of course, if any hitch develops in Congress delaying or reducing American participation in boosted IMF quotas, the situation will be even worse.

There is less than meets the eye in that seemingly huge increase in IMF quotas. On paper, it would appear that an extra $32 billion is generous enough to handle any foreseeable problems.

But only about half of that $32 billion is in hard currencies such as American dollars, German marks, Swiss francs or Japanese yen desirable for international lending. The IMF also will have available an extra $11 billion from standby credit provided for major crises by rich nations through a special borrowing agreement.

De Larosiere's desperate mission shows how badly the IMF is underfunded. (The IMF and many European countries had originally recommended doubling the IMF capitalization to $120 billion.) A few years ago, De Larosiere went hat in hand to Saudi Arabia, and borrowed approximately $12.6 billion, in three $4.2 billion installments, to tide him over until the current planned quota increase was negotiated.

But with the 1981-82 drop in oil prices, Saudi Arabia's excessive wealth has been dented, and the third $4.2 billion installment (which was not a firm commitment) is not certain. The Saudis suggest it is time for the European nations and Japan to ante up some extra money. But these nations tell De Larosiere to meet any Saudi shortfall by "digging into" the quota increase-- which is supposed to handle problems in 1984-88 --and come back later if he needs more money.

So the problem is being swept under the rug. The probable result is a complicated negotiation around the time of the annual meeting, setting new limits on total drawings by any country. If the global economy isn't clearly coming out of a slump, the IMF management may get a go-ahead to beef up its lending kitty by tapping the Eurodollar and other private money markets. Its $35 billion gold hoard provides convenient collateral.