Senators on a banking subcommittee yesterday told bank regulators they favored stricter regulations on foreign loans by U.S. banks, including setting limits on how much a bank may lend to an individual country and establishing new reserves against shaky foreign loans.

Subcommittee Chairman John Heinz (R-Pa.) told bank regulators at hearings yesterday that "it has become apparent to me and several of my colleagues that. . . some regulatory direction is necessary" to go along with an increase in U.S. contributions to the International Monetary Fund. The Reagan administration is seeking to increase the contribution to strengthen the IMF's ability to deal with foreign debt emergencies.

Legislation introduced by Heinz and Sen. William Proxmire (D-Wis.) would allow the Federal Reserve Board to set limits on bank loans to individual countries. It also would make banks write off over the length of a loan the fees they charge when first putting it into place.

Bank regulators appearing before the subcommittee--Federal Reserve Board Chairman Paul A. Volcker, U.S. Comptroller of the Currency C.T. Conover and Chairman of the Federal Deposit Insurance Corporation William M. Isaac--agreed with the senators that further regulation of overseas loans may be desirable, although Volcker appeared less certain about the need for new legislation.

Both Volcker and Conover expressed doubt about whether it would be practical to have overall limits on country exposure.

Conover suggested that more disclosure by the banks of their foreign loans would be a good thing, and proposed that banks should report to regulators on a quarterly instead of a semiannual basis. Heinz supported this idea.

Asked whether the regulators had been forceful enough in the past in cautioning the banks about their overseas lending, Volcker said, "I suppose, in retrospect, probably not."

Isaac said "bank regulators were insufficiently sensitive to the developing problems in foreign lending."

Volcker said the three largest borrowers--Mexico, Brazil and Argentina--had been categorized as "weak" for some time. They are negotiating reschedulings with private banks, and have agreed on loans from the IMF that commit them to austerity measures.

If a country is categorized by the regulators as "weak," then bank examiners comment if a bank has high exposure in that country. Brazil has been in this category for several years, Mexico for about 18 months and Argentina since the outbreak of the Falklands War with Britain last spring, Volcker said.

He appeared more cautious about the need for new legislation than the other two regulators, although he said "the rapid development of international lending and today's problems do point to the need for careful review of present policies and other ideas." He added that "Possible modified or new approaches. . . are under intensive review by the supervisory agencies, and I expect to be able to report conclusions to you in a matter of weeks.

One problem with making it more costly or more difficult now for banks to lend to nations with actual or potential debt problems is that this will make them even less willing to put up new money to help financially striken countries while they adjust. Volcker warned the subcommittee that the chief danger to the system today is not "over-exuberance" in lending, but that "everyone runs for cover so fast that they are mutually destructive."

The IMF has been leaning on the banks to make new money available to Mexico and Brazil as part of the condition for the IMF money. So far these agreements have not yet been completed. Volcker said yesterday that he thought the Mexican loan would be wrapped up in a matter of days. The Brazilian "jumbo loan" was supposed to be completed by Tuesday, but the negotiations are bogged down on the issue of very short-term money that Brazilian banks are borrowing from other banks, sources said.