A six-year study of Cuban and Mexican immigrants shows that the Cubans have adapted better, own more businesses and earn more money than the Mexicans even though they keep more to themselves and are concentrated far more than the Mexicans.

"Spreading new arrivals like Mexicans over the entire United States is not necessarily the best route to go," Dr. Alejandro Portes of the Johns Hopkins University, where the study was directed, said yesterday at a press conference.

"The experience of the Cuban enclave in Miami might spell out a faster way of economic growth for immigrants that could be of greater economic benefit to the U.S. in the long run."

Working with grants from the National Science Foundation, the National Institute of Mental Health and the Ford Foundation, Portes interviewed 822 Mexicans and 590 Cubans who immigrated to the United States in 1973 and followed them up with interviews in 1976 and 1979.

Portes found the overwhelming majority of the Cubans still in Miami where they entered the country, while most of the Mexicans were scattered around the nation even though they came to the United States through Laredo and El Paso, Tex.

"When we asked the Cuban immigrants their intended places of residence, 98 percent responded 'Miami'; six years later, exactly 98 percent were still there," Portes said. "On the other hand, there were Mexican immigrants living in Alaska, Wyoming and North Dakota with major clusters of them in Texas, California and Illinois."

Portes said most of the Cuban immigrants had come to the United States for the first time while most of the Mexican immigrants had already spent time here as illegal aliens.

Said Portes: "Mexican immigration has always been and still is a labor-seeking immigration. Cuban immigration has been and still is a political refugee immigration. Mexico has not suffered a revolution, Cuba has."

Though many began working for less than the Mexicans when they came to the United States, the Cubans have improved their lot faster than the Mexicans. The Cubans followed up by Portes had increased their earnings over $300 a year, excluding inflation, more than the Mexicans had in the six years both groups have been here.

Only one of the Mexicans was self-employed at the end of the six years while one-fifth of the Cubans had their own business. Unemployment was 3.3 percent for the Cubans, 4.4 percent for the Mexicans.

Portes said the main reason the Cubans have done better is that they settled in the Cuban enclave in Miami, where they "were incorporated into a network of economic enterprises already in place that the Mexican immigrants did not have."

The network is made up of 3,000 Cuban-owned business firms in Miami, Portes said, including banks, construction companies, shoe factories, garment makers and cigar factories. The Cuban firms tend to hire only Cubans, Portes went on, especially for the higher-paying and managerial jobs.

Portes compared the Cubans to the Jews who settled on New York's Lower East Side in the early part of the 20th century and "who only hired other Jews for the favored positions."

One reason the Cuban-owned enterprises have thrived, Portes said, is that the newest Cuban immigrants who go to work for them are given the worst jobs at wages that are lower than they can earn outside the enclave.

"So many of the new immigrants are willing to take those jobs because they know there is an upward mobility built into this ethnic solidarity," Portes said. "They know that when the better jobs become available in Cuban firms, they will have an opportunity to get them."