MIAMI -- U.S. immigration investigators say they expect former Panamanian leader Manuel Antonio Noriega to be charged with being at the center of the largest alien-smuggling ring ever uncovered.

Tens of thousands of Chinese, Cubans and other immigrants paid millions of dollars to Panamanian officials to use that nation as an illegal gateway to the United States and Canada, said Robert Harris, chief criminal investigator for the Immigration and Naturalization Service in Miami.

The ring started as early as 1980, and about 4,000 Cubans used it to enter at Miami International Airport alone during the last seven years, authorities said. About 16,000 people were caught "in the pipeline" when the United States invaded Panama in December, said Robert Penland, who recently retired as assistant INS commissioner for anti-smuggling. "Nobody ever operated an alien-smuggling operation to the extent of Panama," Harris said. "It was operated by the government, and it was a well-organized, well-run operation." He said immigration officials could not recall any such state-operated alien trade.

Enough evidence is available to seek indictments, Harris said, but INS and federal prosecutors decided to move cautiously because of the former Panamanian dictator's protracted drug-smuggling case, due to go to trial next year. Any indictment "could be after the trial," he said.