The International Monetary Fund's executive board said tonight it is prepared to give Mexico emergency loans of $300 million to help repair the damage of the Sept. 19 earthquake.

The IMF announcement came as the fund's sister agency, the World Bank, was considering the diversion of a like amount of development loans previously approved for Mexico into emergency aid, according to an official who was in Seoul for the annual meeting of the bank and IMF.

The official said the World Bank has already sent experts in such fields as water supply and waste disposal to Mexico to survey the damage and discuss relief measures.

Shortly before the earthquake, the bank approved a $300 million loan for construction of low-income housing. The official said that Mexico instead might be allowed to spend that money for reconstruction in areas that suffered earthquake damage.

The loans came as the international banking community was assessing the quake's damage and whether it would affect Mexico's ability to service its estimated $96 billion of debt to U.S. and other foreign banks.

Last Tuesday, its commercial bank lenders agreed to postpone for six months a $950 million loan repayment Mexico was scheduled to make in two installments in October and November.

But Mexico told its lenders that it plans to remain current on all interest payments, despite the problems of the earthquake.

Even though Mexico will receive a $300 emergency loan from the IMF, it has been prohibited from making a scheduled borrowing of about $450 million this month under a three-year loan agreement it signed Jan. 1, 1983, with the international financial rescue agency.

The cut-off came before the earthquake, although news of it leaked out the day the disaster struck.

Mexico, long considered the model debtor country, has fallen seriously out of compliance with the economic agreement it reached with the IMF as a condition of the loan. The Mexican budget deficit this year will be about twice as big as projected; it may be higher now as a result of the earthquake. Mexican inflation, which had declined steadily since 1982, also began accelerating again this year.

But Mexico is not alone among Latin American debtor countries and the problems of all the debtors -- whose foreign borrowings total about $360 billion -- are expected to be major topics of discussion at the Seoul conference, which is bringing together about 8,000 bankers, finance officials and journalists from around the world.

The IMF's decision was made at an informal meeting of its executive board today. Disbursement of the money will require a formal request from Mexico first.

The sum, $300 million, is equivalent to 25 percent of Mexico's $1.2 billion capital subscription in the fund. In addition to its normal balance-of-payments financing functions, the IMF has been providing such emergency loans for damage suffered in natural disasters.