The New York businessman in a tan leisure suit was philosophical about his losses. ''We never made any money on our Mexican operation,'' he explained as the plane approached Mexico City. Purpose of his trip: to close out, after 15 years, a plastic wall-coverings plant in Mexico City - and to salvage whatever he could of his investment in an economy now enduring its worst financial crisis since the Great Depression.
But if his plight is typical of that of hundreds of United States businessmen now trying to either disentangle or make the best of their investments in Mexico , so, too, is his optimism.
''We'll do something else in Mexico'' in future years, he says.
Why that confidence?
Despite an economic crisis that many feel has yet to ''bottom out,'' the US business community generally views Mexico's future as remarkably strong.
''We are extremely optimistic about the longer-term potential of the Mexican consumer economy,'' says Gaston Levy, general manager of the Latin America division of the Gillette Company, which has three factories in Mexico. But right now, he says, ''We're just waiting - nothing is clear enough for us to move.''
''There are tremendous numbers of (foreign businessmen in Mexico) who are looking for any opportunity to sell out and get out,'' says Willard Andrews, president of the Mexican Chamber of Commerce of the United States and president of the Latin American division of the New Jersey-based Becton-Dickinson & Co.
Mr. Andrews sees ''no economic recovery'' in sight for 1983. But he says that in the long term, ''there isn't the slightest doubt that Mexico is going to come back.''
Most frustrating for US businessmen in the short term are the currency exchange controls imposed by the Mexican government. They are designed to keep dollars - desperately needed to help repay the country's international debt, which is about $85 billion - from flowing out of the country.
But the controls have produced devastating side effects on the nation's manufacturing sector. Mexican firms find it extremely difficult to pay dollars for much-needed imports of raw or semi-finished materials. And few international suppliers will accept payment in the deeply devalued peso.
The result: Many firms are slowly starving for lack of such simple materials as plastic and steel, say economists and manufacturers familiar with the region. They say this adds to the nation's already high unemployment, and further dampens the economy.
Even when such materials are available just across the border, ''No US exporter is doing any exporting (of goods to Mexico) unless there is cash in the hand,'' says Alfredo V. Restrepo, the Bank of Boston's vice-president for Mexico and Central America.
Where do American businessmen see the Mexican economy headed in the short term?
* Inflation. Corporate planners use predictions for 1983 ranging all the way from 90 percent to 200 percent. Most favor the lower figure. The new Mexican government of President Miguel de la Madrid Hurtado has made fighting inflation its ''top priority,'' says the head of one international businessmen's group in Mexico City, ''and they've got an awful lot of power.''
* Exchange rate. The dollar now buys about 150 pesos - a sixfold devaluation from the 25-to-1 rate prevailing just over a year ago. The expectation among many US businessmen is for a stable rate through midsummer, followed by a further devaluation, which could bring the peso as low as 230 to the dollar by year's end.
* Growth. Between 1971 and 1981, the nation's gross domestic product (GDP) averaged about 6.5 percent growth each year. Figures for 1982 - following the plunge in the price of oil - show roughly zero growth. Mr. Andrews foresees 1983 GDP ''growth'' at minus 5.5 percent.
* Debt. ''We do expect that before the end of the year the Mexican government will have to come into the marketplace for additional financing,'' says Mr. Restrepo - a view generally shared among US economists and bankers.Still unclear , however, is the size of the new loans. Analysts say they could be anywhere from $2 billion to $7 billion, depending on Mexico's success in meeting fiscal and monetary conditions set by the International Monetary Fund. The IMF reportedly has told Mexico that its economic performance for the first quarter of 1983 is in line with the IMF target.
With all these problems, why does Mr. Andrews still see Mexico as a solid investment opportunity?
He ticks off several positive factors which, he says, will survive the current economic crisis: a large (75 million), youthful, and growing population of customers for US exports; immense and ''purposely understated'' petroleum reserves; increasing tourism; and the long-term stability of the Mexican government, which, unlike many in Latin America, regularly changes its leaders without coups.
He also cites the willingness of the Mexican population to make major sacrifices. Former Mexican Finance Minister David Ibarra agrees. Speaking to a group of US editors and scholars at a conference in Washington recently, he noted that the reaction among Mexican workers to ''a dramatic reduction of real wages'' has so far been ''very, very minor,'' and that they have shown ''unusual patience.''
He agrees, however, that there is a potential for social unrest, and notes that ''the middle classes will show an increasing dissatisfaction'' with the new economic hardships.
But one former high-level Mexican government official, speaking to the same group, noted that Mexican institutions are stable enough that there will be ''no major disruption in the social climate.''