A senior U.S. immigration agent was sentenced in Hong Kong to 40 months in prison yesterday after pleading guilty to involvement in a Chinese alien-smuggling ring.

Jerry Wolf Stuchiner, 45, a veteran investigator with the Immigration and Naturalization Service (INS), was arrested July 15 upon arrival at Hong Kong's Kai Tak airport with five forged Honduran passports.

At the time of his arrest by Hong Kong anti-corruption agents, Stuchiner headed the INS office in Tegucigalpa, Honduras, and was the only U.S. immigration investigator based in Central America. He previously had served in Hong Kong from 1989 to 1994 and was considered one of the agency's top experts on the smuggling of Chinese illegal aliens to the United States, an estimated $3.5 billion-a-year business that brings up to 50,000 Chinese annually to this country, according to a recent government study.

Stuchiner's crime, the equivalent in the INS of a major spy defection, has prompted an investigation by the CIA and Justice Department to determine how many illegal aliens may have been smuggled as a result of his activities, an informed official said.

The case is the latest in a series of incidents that have embarrassed the INS at a time when it says it is making progress in curbing illegal immigration and breaking up major smuggling operations.

In June, four senior INS managers were reassigned after a Justice Department investigation found that they had released or transferred dozens of detained illegal aliens as part of an elaborate attempt to deceive a congressional fact-finding delegation during a visit to Miami.

Last month, John Lonergan, the assistant INS district director in Newark, N.J., was indicted on corruption charges.

In San Diego, a union leader in the Border Patrol, a branch of the INS, accused managers of falsifying arrest records and intelligence reports to portray a border-control program called Operation Gatekeeper as a success. INS Commissioner Doris M. Meissner ordered an investigation into the allegations, which so far have not been substantiated, officials said.

Stuchiner, a 19-year INS veteran,, had been instrumental last year in breaking up a major alien-smuggling ring allegedly headed by a Costa Rican woman, Gloria Canales, who was accused of moving thousands of Chinese and Indians through Central America to the United States.

After Stuchiner's arrest, the Honduran government suspended its immigration chief, Angelina Ulloa de Venis, her deputy and five other officials on suspicion of selling forged Honduran passports to Asians seeking to enter the United States illegally. Ulloa has denied the allegations, saying she was "startled" by the arrest of Stuchiner, with whom she had worked closely on the Canales investigation.

Hong Kong authorities said Stuchiner admitted that he was delivering the five Honduran passports, which contained a seal and signature but were otherwise blank, to the Honduran consul general in the British colony. The diplomat, Herby Weizenblut, was briefly detained by Hong Kong agents, then released. He has since disappeared, and his whereabouts are unknown, officials said.

Stuchiner's defense attorney, Gary Plowman, acknowledged that the INS agent had been a "courier with knowledge," whose actions were "certainly irrational and stupid for a man who had spent his lifetime upholding the law." He would not comment on his client's relationship with Weizenblut or on what Stuchiner stood to gain by delivering the passports.

In court, Plowman presented letters and faxes commending Stuchiner. Many of them were from Jewish organizations grateful for the role he played at the U.S. Embassy in Vienna from 1985 to 1989 in helping Jewish refugees flee Iran during the rule of Ayatollah Ruhollah Khomeini.

In sentencing Stuchiner the judge said he had committed "a gross breach of trust," but that she was reducing his prison term from the six years she had originally set. She said she took off two years because he had pleaded guilty from the start, then deducted an additional eight months because he previously had maintained a good professional record and had lost his health insurance and pension. Staff researcher Jenni Lau in Hong Kong contributed to this report.