LOS ANGELES, NOV. 14 -- Illegal migration from Mexico to the United States has become so central to the needs of Mexican families and communities -- and some American businesses -- that restrictive new U.S. laws are unlikely to end it, according to a study of four Mexican communities.

"Viewing international migration as a developmental social process suggests that any change in the status quo will be very difficult to achieve," concluded the study, being published by the University of California Press. " . . . The momentum of migration is strongly resistant to change," it said.

Sociologist Douglas S. Massey of the University of Chicago and anthropologists Rafael Alarcon of the Colegio de Jalisco, Jorge Durand of the Colegio de Michoacan and Humberto Gonzalez of the Colegio del Bajio said they found that migration has deep economic, social and demographic roots. More than 80 percent of some rural families' income comes from relatives working in the United States, they said. Fiestas in Mexico and soccer clubs in the United States provide social links at both ends of the migration route.

"After 40 years, international migration has become so institutionalized, routine and embedded into the social and economic fabrics of both countries that the human and financial costs of stopping it are probably prohibitive," they concluded. "In spite of all the rhetoric, few people on either side of the border seem willing to pay the costs of stemming the flow."

The U.S. Immigration Reform and Control Act of 1986 created new penalties for American employers who knowingly hire illegal aliens. The number of Border Patrol and immigration officers also has grown substantially in the effort to curtail the flow of migrants.

The study showed that workers from both urban and rural Mexican communities can earn five to 10 times their Mexican incomes in relatively low-paid American jobs. The money, sent back to Mexico, stimulates home building and the birth of small private businesses.

The study shows that the Mexican communities first send out a few migrants who establish contacts with U.S. employers and community groups, making migration much easier for friends and relatives who follow.

Interviews were conducted in 1982-83, Massey said in an interview, but the results suggest that no matter what new restrictions are imposed, the flow of migrants "is much easier to start than to stop."