BOSTON (AP) _ The First National Bank of Boston broke its silence Thursday on its multimillion-dollar dealings with a reputed mob family, blaming several midlevel employees for ''very poor judgment'' that may have allowed the bank to unwittingly be used by organized crime.

Chairman William L. Brown told reporters the bank gained nothing - ''not one dime, not one gratuity'' - by its dealings with the family of Gennaro Angiulo, considered the head of New England's most powerful organized crime network.

Brown said employees made an innocent mistake and used ''very poor judgment'' when they placed two real estate companies owned by the Angiulos on a list that exempted their large cash transactions from government scrutiny.

''Just because we're big doesn't mean we don't make mistakes,'' Brown said. ''You're assuming all our employees are perfect and they are not.''

He said if the Angiulos, who conducted $7.3 million in transactions at the bank between 1979 and 1983, were using the bank for laundering mob money, then the bank was unwittingly used for unlawful purposes.

But he added, ''I have not found the Angiulos guilty of anything. That's up to the court.'' Angiulo faces a trial next month on federal loansharking and racketeering charges.

Brown refused to identify the branch manager and other employees responsible for putting the Angiulo companies on the exempt list, and said no one had been fired, transferred or disciplined.

''We're not trying to find a scapegoat,'' he said. ''We will take care of the discipline down the road.''

The Bank of Boston, the country's 16th-largest bank-holding company with $22 billion in assets, pleaded guilty two weeks ago to not reporting $1.2 billion in cash transactions with nine foreign banks. It paid a $500,000 fine, the largest ever levied for violating federal currency-reportin g regulations.

Shortly after the bank paid the fine, investigators confirmed published reports that the Bank of Boston had placed the Angiulos on its exempt list, which is legally reserved for retail outlets that ordinarily deal in large amounts of cash, such as supermarkets and sports arenas.

If a company is not on the list, bank employees must notify the Treasury Department every time the company makes a cash transaction larger than $10,000. The regulation was designed to crack down on money laundering by organized crime figures and drug dealers.

There is no known connection between the unreported international transactions and the Angiulo family.

Brown said that as a result of the Angiulo case, the bank now has several high-level bank officers review all applicants for the exempt list and has tightened the requirements to get onto the list.