Mexican officials may seek to postpone $1.6 billion in interest payments to private creditors this year, sources said today, a proposal that bankers warn could upset Mexico's quest for new loans from commercial lenders.

In a closed-door meeting Thursday with the Business Coordinating Council, Mexico's leading private business association, Finance Minister Jesus Silva Herzog said the government may negotiate the "suspension" of nearly half the $3.5 billion in interest he said Mexico is slated to pay commercial creditors in the second half of 1986.

The finance minister's statements, which a ministry official said today "were intended to be confidential," were prominently displayed in Mexican newspapers this morning. The press reports of Silva Herzog's remarks were "incomplete, but essentially accurate," the official said.

"Negotiations with Mexico always start with a surprise," a New York banker said today, adding that creditors are unlikely to accept a substantial interest deferral.

If Mexico successfully concludes its negotiations for a loan from the International Monetary Fund, private banks said they will begin formally discussing Mexico's request for commercial credits. Until recently, bankers and Mexican officials said the nation would ask for between $2.5 billion and $2.7 billion in fresh loans, but some bankers interviewed in past weeks say they now expect Mexico to seek up to $3.5 billion from private lenders. The IMF loan is expected to be between $1.3 billion and $1.5 billion.

As commercial loan negotiations proceed, "The first thing the banks will want is for Mexico to keep up its interest payments," the banker said in a telephone interview. "It is hard to get new money if you aren't up to date with debts you already have."

Silva Herzog plans to travel to Washington next week for talks with the IMF and U.S. Treasury officials, finance ministry spokesmen said. Banking sources said Silva Herzog might meet with Citibank executive William R. Rhodes, who is chairman of the committee of commercial banks that negotiates with Mexico.

Any partial suspension of interest payments would not be unilateral, Silva Herzog is said to have stressed in his meeting with the Mexican businessmen. It would be a negotiated "temporary" agreement, he said. He also reportedly assured them that negotiations are progressing with the IMF.

With political pressure mounting for the government to stop debt payments, many leading Mexican businessmen have voiced concern that such a move would cut off future sources of foreign financing for private enterprise here.

"It is better to negotiate than to declare yourself bankrupt," Bernardo Ardavin, president of the Mexican Employers Confederation, said in a press conference Thursday. The business community agrees with the government, however, that foreign debt payments "have to be based on the real possibilities of the national economy," Ardavin said.

Mexico's foreign debt now totals some $97.5 billion, of which the government directly owes $72.5 billion. In the first quarter of 1986, Mexico paid $1.46 billion in interest on its public-sector debt, the finance ministry reported. Payments scheduled for the year's second and third quarters are said by bankers to be marginally higher.

Falling interest rates are expected to lower Mexico's total 1986 interest bill to perhaps $1 billion less than the $9.9 billion it paid last year. But because of falling oil income, the cost this year of Mexico's debt servicing -- interest plus principal payments -- will rise as a fraction of export earnings substantially above last year's 60 percent, a share already termed "intolerable" by Mexican leaders.

But all estimates are based on assumptions about oil prices. Some economists think oil prices will rise enough to keep Mexico's overall debt burden from rising.

Government officials have insisted repeatedly in recent weeks that they would be seeking unspecified concessions from private banks that would substantially reduce this year's debt payments. Some finance ministry advisers say they favor a "Peruvian-style" plan to link debt servicing to some 25 percent of Mexico's foreign-exchange income or, alternatively, half of the country's petroleum earnings.

"They absolutely have to offer us something," one senior economic policy maker said recently. "The banks defend their stockholders' interests, and we have been defending Mexico's interests. We think Mexico has been hurt enough and that now it is time for the stockholders to suffer."

One concession creditors are prepared to offer, foreign bankers here say, is a further postponement of a $950 million principal payment originally scheduled for March and now pushed to September.

In addition, one U.S. banker said, creditors are willing to reduce the profit margin (called a "spread") that banks tack on to their cost of funds to determine the interest rate Mexico must pay on the $48 billion government debt package it rescheduled in August.

In 1987, the rate Mexico pays is slated to rise to 1 1/8 percentage points above the so-called London Interbank Offered Rate, a basic measure of the cost of funds to banks, from 0.875 percentage point today. But bankers said they "expect Mexico to demand and get" a reduction to perhaps 0.5 percentage point above LIBOR next year, the banker said.

But proposals to defer or capitalize large interest payments "are unacceptable, because they are tantamount to default," said the banker, who has represented a major bank on the commercial creditor steering committee.

Mexico's foreign-exchange reserves have remained relatively close to the $5 billion reported at the end of last year, bankers and diplomatic analysts said.