Mexico's finance minister began meetings with U.S. bankers in New York yesterday, reportedly seeking to delay payment on some of Mexico's huge external debt in the wake of the financial crisis that has sent money flooding out of the country.

Officials of about 100 American banks are due to meet with Finance Minister Jesus Silva Herzog and federal regulators in the New York Federal Reserve bank today, sources said. The meeting was requested by the Mexicans, who also are negotiating emergency credit lines from central banks and international agencies this week, sources said.

The New York Federal Reserve Bank yesterday took the unusual step of denying that it was holding an emergency meeting on Mexican loans. The denial followed a sharp drop in the stock market as rumors spread that some large U.S. banks could be in trouble because of their Mexican loans. The market later recovered, and bankers denied that there was any likelihood of default by Mexico.

A flight of capital from Mexico and apparent collapse of confidence in the heavily indebted Mexican economy has sent tremors through the international banking community in the past few days. Mexico has a huge volume of external debt -- estimated by banking sources at close to $80 billion -- much of which was taken on when strong oil prices encouraged bankers to lend to the oil-rich country.

However, one banker said that about $10 billion to $12 billion of the $80 billion is at issue in the current discussions with the U.S. bankers. He denied that the Mexicans were seeking a freeze on all payments of debt principal, saying "what happened was a large bubble of short-term debt" built up by the Mexicans during 1981, which they are "at the moment not able to take care of." Herzog is expected to ask to have this debt rescheduled so that it can be paid back over several years.

Among the U.S. banks reported to have heavy exposure in Mexico are Manufacturers Hanover Trust Co., Bank of America, Chase Manhattan and Citibank. Most large U.S. banks have some loans in the country because it has been such an enormous borrower on international capital markets.

However, as fears about the weakness of the Mexican economy have grown, bankers have become much more reluctant to lend to the country. As new credit dried up and two devaluations this year failed to stop money leaving the country, the Mexicans were forced last week to close their foreign exchange markets and go to the international banking community for cash.

The Reagan administration has declared its willingness to help Mexico, and Treasury Secretary Donald T. Regan said this week he was "very happy" that the Mexicans are seeking a loan from the International Monetary Fund. Any loan from the IMF would come with strings attached, which likely would require the Mexican government to institute an austerity plan aimed at narrowing its balance-of-payments deficit and curbing its soaring inflation rate.

The Mexican peso fluctuated wildly on foreign exchange markets yesterday when the government reopened exchanges after the week-long shutdown. The free market in pesos saw the rate sink as low as 130 to the dollar in Mexico City compared with a rate of just under 70 to the dollar when the markets were closed last Thursday.

A banking source said that Herzog comes with some proposals in hand. One of them suggests that Mexico will increase oil production and in return ask for advance payment from some industrial countries for at least part of the oil. It is "extremely critical" for Mexico that there should not be a further weakening of the oil market, one New York banker said yesterday. The oil glut was largely responsible for Mexico's current financial problems, some experts believe.

With sharply reduced prospects for oil earnings, Mexico has become unable to continue financing ambitious development programs begun in the oil boom.

One international official commented that the biggest danger to the banking system was the self-fulfilling prophecy that the nation would be unable to repay debts, which in turn would dry up the flow of new money that it needs in order to repay existing debts and buy imports.