Two Armenians were busted as part of a multimillion-dollar plot to ship shoulder-to-air missiles into the United States that could be used by terrorists to shoot down airplanes, federal authorities announced yesterday. Eighteen other people involved in the scheme were arrested earlier this week in New York, Los Angeles and Miami. "There have been two additional arrests made by Armenian authorities based on information we provided them concerning the supply of weapons," Assistant U.S. Attorney Benjamin Lawsky said during a hearing yesterday in Manhattan federal court. "This just shows that the plot wasn't just talk. These were real weapons with real people planning to ship them," Lawsky said. The two Armenians arrested were Vahajn Yeribekyan, 25, and Razmik Barsenghyan, 32. It is believed that the pair had photographed rocket-propelled grenade launchers, shoulder-to-air missiles and other Russian weapons they planned to smuggle into the United States through co-conspirators here. What they didn't know is that the FBI had conducted a sting on arms smuggling, and the buyer they were dealing with was an informant. The investigation continues. "We are working with our counterparts overseas to get the weapons," Manhattan U.S. Attorney David Kelley said.