When Harvey Blumenthal of Chevy Chase met Vietnamese refugee Bang Thuy Bui in 1976, Bui told of having a treasure of $5 million in cash, Picasso paintings, jewels and gold that he had shipped to France before the collapse of the American-backed government in his homeland. According to court records, Bui claimed he used part of the money to buy an estate on the French Riviera and used some more to buy a bakery in Arlington.

Over the next five years, Blumenthal gave Bui more than $750,000, deposited in an assortment of bank accounts, supposedly to help Bui pay taxes, fines and other penalties so he could free the bulk of his French assets, court records say.

Blumenthal received telephone calls from what he believed were French bankers and customs officials vouching for Bui's accounts, and later from French judges and prosecutors who said Bui faced criminal charges there for illegal transfer of assets and bribes in connection with an attempt to retrieve his treasure. Blumenthal received daily calls from Bui, purportedly from the Central Prison of Paris.

Yesterday, Bui was arrested by FBI agents at a bank in Washington -- but not for any misdeeds overseas. A complaint in U.S. District Court here charged Bui with wire fraud in connection with $10,000 that he received from Blumenthal, allegedly to pay fees to the Paris customs office.

A detailed, sworn statement filed with the court by FBI special agent John R. Oller described a complicated scheme, based on telephone calls, with which the FBI alleges Bui bilked Blumenthal out of his $750,000.

"This has been a terrible situation," said Blumenthal, a former restaurateur who met Bui over a deal for some egg rolls. Blumenthal declined to comment on the case "until the dust clears."

U.S. Magistrate Jean F. Dwyer ordered that Bui be held on a $100,000 cash bond and directed that he also put up his Virginia home in Vienna as collateral if he wants to get out of jail on bond.

Blumenthal went to the FBI last November after discussing with a lawyer his business dealings with Bui. From there, the FBI followed Bui to coin-operated telephones in bowling alleys, laundromats, hotel lobbies and gas stations where Bui allegedly telephoned Blumenthal, impersonating French officials who were supposed to be calling from France and himself pretending to be in a French jail.

Last Dec. 3, an FBI agent stood next to Bui at a telephone booth in the Sheraton Carlton Hotel at 16th and K streets NW while Bui allegedly called Blumenthal and said he was calling from a Paris prison. Early that same day, Bui was seen by the FBI at a pay telephone booth at a gas station on Chain Bridge Road in Fairfax County, according to court records. Minutes after Bui hung up, the FBI called Blumenthal, who said he had just finished speaking with a Judge "Brugyiere" in Paris, court records said.

At one point in the summer of 1980, Blumenthal put $1,500 under a trash can outside the Sears department store in Northwest Washington after he got a telehone call -- purportedly from a French Embassy official -- who said the money was needed to pay a bribe to release Bui's assets.

When Blumenthal got home, he got another call. This time it supposedly was another French official, who said that Blumenthal had been photographed dropping off the money, that the person who picked it up had been arrested and that French courts would be notified of Blumenthal's activities, court records said.