A Washington businessman who owns a travel agency and two limousine leasing firms is a key figure in a federal grand jury investigation of an alleged bad-check scheme that law enforcement officials say bilked the American Security Bank of about $3.2 million--about $1 million more than the bank had initially estimated.

Ibrahim Awadllah, 46, owner of Intra-World Travel Inc., Capitol Limousine & Sightseeing Service and Watergate Limousine Service, is considered a principal figure in the bank case, law enforcement sources said yesterday.

Raymond C. Mowchan, who resigned two weeks ago as vice president of the bank's Woodley Park branch, also is under investigation, law enforcement officials said yesterday.

According to one source, the investigation is looking into whether Mowchan issued a series of cashier's checks to Awadllah over 2 1/2 years totaling about $3.2 million, and whether Awadllah, in exchange for the checks, gave the bank personal or business checks drawn against accounts that either had been closed or contained insufficient funds.

Awadllah said in an interview yesterday that he knows that he is under investigation, but that he has done nothing illegal.

"I'm not guilty," he said. "Maybe I made a mistake, but I'm not guilty."

Awadllah insisted that another person, who law enforcement officials say is not a subject of the investigation, took part as well.

"Maybe I'm involved, but some big businessman more important than me is involved," he said. "He's the man in charge . . . If you put my name in the paper alone, it will be wrong."

Awadllah described the man, who has operated small businesses in Washington and elsewhere, as a "loan shark" with whom he has done business, off and on, during the past six years.

Mowchan, 38, said in an interview last week that he had not benefited personally from the transactions. He said that his difficulties at the bank arose after he failed to notify his superiors when he discovered that the customer--whom Mowchan would only describe as a "Jordanian businessman"--had improperly obtained a loan and had written bad checks. Awadllah is a Jordanian who grew up in Jerusalem and who came to this county in the early 1950s.

Mowchan said he wanted to give the customer, with whom he said he had no personal relationship, a chance to quietly repay the bank, but that the customer in turn wrote more bad checks to cover his bad debts.

Last week, law enforcement officials said that a loan may have been involved. Yesterday, however, a source said investigators had no knowledge of any loan being part of the alleged scheme.

American Security, the city's second largest bank, called in the FBI two weeks ago after the bank's internal monitoring system detected what the bank later described as "suspicious cash transactions" at the Woodley Park branch, at Connecticut Avenue and Calvert Street NW.

Last Wednesday, following a preliminary investigation by the FBI, American Security issued a statement announcing that one of its officers had made "unauthorized and unlawful cash disbursments" to a customer "in excess of $2 million."

Yesterday, the law enforcment source estimated the bank's losses at $3.2 million. "We won't know until we look at all the bank records" that were subpoenaed by a federal grand jury looking in to the case, the source said.

A vice president of American Security said yesterday that the bank would have no further comment on the case, pending the outcome of the investigation.

Walter B. Connolly Jr., a Washington attorney representing Awadllah in the investigation, emphasized that the federal investigation had only recently begun and that his client has not been formally charged with any wrongdoing.

"I'm representing him on some issues presently pending," he said. "Whether he is a party to what occurred at the bank has not been alleged . . . I don't think it's a good idea to be commenting on cases that are pending."