The FBI is investigating a complaint by the brokerage firm of Merrill Lynch that a man deposited a worthless check for almost $500,000 in an account at their Tysons Corner office. Before the firm learned that the check was bad, Merrill Lynch had paid out "a large sum of money" from that account, the FBI said yesterday.

Merrill Lynch was reported to have fired at least two employes of the Tysons Corner office as a result. A spokesman for Merrill Lynch in New York confirmed the firings, saying the reason was that "we did not think they performed their jobs up to our standards."

Gordon F. Linke, manager of Merrill Lynch's Tysons Corner office, declined to discuss the case.

Steve Pomerantz, assistant special agent in charge of the Northern Virginia field office, said that the FBI has suspects and hopes to be able to file charges "in the near future" against individuals who were not identified.

The FBI said a check deposited at Merrill Lynch in August was a cashier's check drawn on a foreign bank. Other sources reported that the bank was located in the Marshall Islands, a Trust Territory of the Pacific, administered by the United States. The Marshall Islands are about 2,500 miles southwest of Hawaii.

Sources said that the money withdrawn from Merrill Lynch may have been used to open an account at Prudential Bache's office at Tysons Corner. Sources said that an account was opened there in mid-August with a Merrill Lynch check for $421,000. About three weeks later, the funds were withdrawn and wired to a bank in Northern Virginia.

Fred Rose, manager of the Prudential Bache office in Tysons Corner, said he would have no comment.

The Merrill Lynch episode was cloaked by the reluctance of those involved in the case to provide details. A variety of sources identified the people fired as a broker and an operations manager.

A third person, a cashier, was transferred from the Merrill Lynch office at Tysons Corner to another branch.