As many as 3,000 illegal aliens, most of them North and South Koreans who used Argentina as a way station, may have entered the United States with False U.S. visas they purchased from a bogus "parallel" American consulate operating here for a year before being closed 10 days ago.

Among those arrested by Argentine police in connection with the "consulate", and the visa ring that operated it, were four Argentine employes of the official U.S. Consulate here. They were charged with participating in what diplomatic observers said could turn out to be the largest visa scandal in this history of U.S. consulates aboard.

Although it cannot be determined exactly who used the visas to enter the United States illegally, officials say some of those who purchased the fradulent travel documents were refugees from North Korea.

One U.S. diplomat here acknowledged the possibility that North Korean espionage agents could have been among those who bought the fake visas. The diplomat said, however, the possibility is nothing more than conjecture.

A spokesman for U.S. Ambassador Rayl castro said that the ring had destroyed whatever records it kept and that it would therefore be impossible to determine the exact names and numbers of the persons using the falsified visas. The embassy spokesman said that it is assumed that most of those who obtained the fraudulent visas-at least 1,000 and possibly as many as 3,000 persons, according to those arrested-have already used them to enter the United States.

Argentine police estimate that the visa ring may have taken in as much as $5 million by providing false travel papers to thousands of persons who paid between $1,000 and $3,000 each to have their passports stamped with the U.S. Embassy official visa stamp.

The stamp was available to member of the ring employed in the consulate as assistants to American consular officials, according to a police account that was confirmed by the embassy.

These assistants, working with other members of the ring who operated travel agencies or who had connections in a small section of Buenos Aires called "Koreatown", usually provided visas to persons otherwise ineligible to enter the United States, either as tourists or as immigrants.

In some cases, according to police, persons who might have been eligible for visas were told that they were not or were told that the paperwork would take a long time. Then, the members of the ring working in the official consulate would refer those seeking legal travel documents to the "parallel consulate," located only four blocks from the embassy, in the home of Ricardo Luque, one of the consulate employes who was allegedly a member of the visa ring, officials said.

The spokesman pointed out that once illegal immigrants are in the United States they cannot be identified and extradited because it is unconstitutional for U.S. authorities to ask to see a person's visa unless they have clear reason to suspect wrongdoing. Only if the illegal alien is arrested on another charge may police in the United States call in federal immigrations officials if they have reason to suspect that the person under arrest has entered the country illegally.

According to Argentine police, who were called in by the embassy Feb. 12 after American consular officials here discovered that a blank U.S. passport was missing several months ago, most of the Koreans who ultimately left for the United States had first entered Argentina illegally.

After a seven-week investigation, internal security agents sent from Washington by the State Department arrested more than a dozen members of the ring March 20. At least two of those arrested, inlcuding Luque, who worked in the embassy for six years before his arrest and dismissal, are still in jail.

The embassy spokesman stressed that none of those arrested were Americans. Almost all were Argentine citizens except for two Korean nationals living legally in Buenos Aires.

As a result of the arrests and attendant scandal, embassy officials said the security agents sent from Washington are still studying how the ring could have operated for so long without being detected. New procedures will be implemented to guard against a repetition of the incident, the embassy said.

The U.S. consulate here processes between 500 and 800 visas a day, making it one of the busiest in the world. Argentines have been traveling to the United States in record numbers this past year because of inflation in Argentina and favorable exchange rates for the peso against the dollar.

The embassy, obviously embarrassed by the ring that operated for at least a year before its discovery, has been extremely reluctant to give details beyond those Argentine police have provided about the incident.

But one veteran U.S. diplomat said he could not remember a visa scandal of this magnitude occuring before in a U.S. consulate.