Defying risk of arrest as an illegal alien, a 24-year-old Mexican farm worker told a Senate committee yesterday how he was recruited as a "strike-breaker" for the California lettuce fields.

His testimony, translated from Spanish as he went along, was delivered against a backdrop of continuing recriminations between the United Farm Workers and the Carter administration. At issue are illegal aliens who allegedly are being used to break the UFW's four-month-old lettuce strike.

UFW President Cesar Chavez, reiterating earlier charges, told the Senate Labor and Human Resources Committee that the U.S. Immigration and Naturalization Service is prolonging the strike by refusing to crack down on illegal immigrants used as replacement workers in the struck fields.

In a direct clash with Leonel J. Castillo, the head of the immigration servive and one of the administration's highest-ranking Hispanic appointees, Chavez charged that the use of alien strikebreakers is more pervasive now than ever before in the bitter history of West Coast agricultural strikes.

Castillo, appearing later in the hearing, said 8,319 arrests, more than twice last years's total of 4,100, were recorded in California's San Joaquin and Salinas valleys over the past month, including 442 based on complaints filed by the UFW.

Committee Chairman Harrison Williams (D.N.J.) began his dialogue with Castillo by questioning INS' "vigilance" in pursuing illegal aliens into the struck fields but wound up praising Castillo's performance.

A rather stoic figure amid the cross fire, Luis Gonzales, who had been brought by Chavez to testify on strike-breaking efforts, told the committee he had left his home in central Mexico to find work in the United States because he needed money for his pregnant wife.

Gonzales said he met a man named Francisco at a park in the border town of Mexicali, and Francisco offered to arrange a trip across the border into California. He was then driven to near the border, told how to scramble across and then met on the other side by Francisco and Francisco's foreman. who drove him several hundred miles north to the Salinas lettuce fields, Gonzales said.

When the bus in which they were traveling caught fire, he said, they moved into a van that had been following them.

At the fields, which he identified as belonging to Sun Harvest Inc., the main strike target, Gonzales said a company employe supplied him and other workers with Social Secruity numbers to put on registration papers.

The next day, he said, he worked until the noon lunchbreak when three UFW workers told him about the strike and suggested he could find work elsewhere. He said he left then.

Gonzales said he has been able to send $150 to his wife and later told reporters it was given to him by the UFW.

Gonzales is under subpoena to testify before the California Agricultural Labor Relations Board, and Castillo said that, under an agreement with the board, Gonzales will not be deported until after the hearing. But then, Castillo said, he will face deportation.