Three states have signed up for an Immigration and Naturalization Service pilot program that allows state welfare or unemployment benefit offices to search through the INS' computerized records to determine whether a foreign applicant is listed as a legal U.S. resident and thus is eligible for benefits.

However, only Colorado has started to use the checking system; Illinois has not installed the necessary computer terminals and California law obliges the unemployment benefits office to draft regulations informing the public of the new program before it can go ahead with the computer checks.

Almost all state unemployment laws and the regulations governing such federal programs as Medicaid, food stamps, welfare and subsidized housing deny benefits to illegal aliens.

According to Steven Siem, an official in Colorado's unemployment office, about 140 of the 2,300 foreigners applying for benefits this year have been rejected; more than 80 percent of the rejections came after prescreening with the INS computer indicated that the applicants were not on an INS list of 18 million legal foreign residents.

"We have been able to intercede and intercept claims that would otherwise have been paid . . . . We're reasonably pleased with the results," said Robert Hase, who runs Colorado's unemployment insurance program.

Previously, most states checked the status of foreign applicants by a time-consuming process of mailing forms to the INS, asking that applicants' information be verified.

If a foreign applicant is not listed on the INS computer, state officials ask him to check his status with the INS office. Usually, INS Associate Commissioner John W. Murray said, those rejected do not contact INS. "We do not go after them," he added.

Jerry Berman, an expert on privacy and computerized records for the American Civil Liberties Union said that he had no objection to the system of screening applicants for welfare or unemployment benefits with the INS computer.