Because of growing international financial tensions, the United States and other major powers appear ready to accelerate the timetable for expanding lendable resources of the International Monetary Fund.

"The chances are now better than even" that the IMF's Interim Committee will meet here in late February, instead of April, to nail down an additional aid package for Third World countries worth about $30 billion, a key official said.

Changing an Interim Committee date would be unprecedented. Willingness of the First World countries to cope with the debt problem is counted on to give a psychological boost to the international financial community and encourage commercial banks not to cut back their own loans too sharply.

Meanwhile, negotiations for a large IMF loan to Mexico reportedly are on track. Formal announcement is planned for the week of Dec. 20.

The exact nature of the projected boost in IMF resources will be determined at two preliminary meetings in Europe next week.

First, Treasury Secretary Donald T. Regan and Federal Reserve Board Chairman Paul Volcker will meet on Thursday with their counterparts from West Germany, France, Great Britain and Japan outside of Frankfurt. After this Group of Five session, the Group of 10 deputy finance ministers will meet the next day in Paris.

They are expected to agree on at least a 40 percent increase in IMF quotas--deposits by the member countries--and an expansion of the General Agreements to Borrow (GAB) lending authority from about $6.5 billion to at least $20 billion.

Although West Germany and some other major donors, anxious about the precarious state of the Third World economies, have been anxious to boost IMF quotas by at least 50 percent, the United States so far has clung tenaciously to an outside figure of 40 percent. "But there has been no final decision," an American source stressed.

Present IMF quotas, scheduled to last through 1985, now total 61 billion special drawing rights, worth approximately $65 billion. A 40 percent increase would add about $26 billion, about half of which would be in currencies appropriate for IMF lending to poor countries.

This infusion of $13 billion, added to the boost in GAB resources--which under present plans would become available to countries other than the G-10 (the present rule) -- would make up the package.

But the problem is exceedingly complicated, and many details are yet to be worked out. For example, the member countries put up 75 percent of their quota in local currencies, with 25 percent in SDRs or in hard currencies. "But not too many countries have that 25 percent at hand," an IMF source pointed out.