A Northwest Washington man whose bank balance at one point reached six figures when it should have been three because of a computer error was arrested on a theft charge yesterday after checks totaling six figures were written against the account, D.C. police reported.

On March 12, police said, the National Savings & Trust Co. showed a balance of $171 in the account of Michael Caldwell Fleming in the name of Fleming Enterprises. That day, they said, Fleming, 35, of 4201 Massachusetts Ave. NW, deposited a $221 check into the account.

Rather than add the $221 to the $171 to compute the balance, however, the bank's computer added $212,000, according to the report of a detective in the police check and fraud unit.

Between the day of the deposit and yesterday, Det. Donald Kaufman said in the report, 15 checks were written against the account, totaling $212,004.99.

Yesterday, police said, a man entered the NS&T office at 15th Street and New York Avenue NW and attempted to cash a cashier's check for $100,000. Police said bank authorities had by that time been alerted to the discrepancy in Fleming's account, and the man, identified later as Fleming, was detained.

They said they charged Fleming with first-degree theft.

Fleming was released under $2,000 cash bond pending arraignment in Superior Court today.

Fleming could not be reached for comment.

Benjamin O. Wood Jr., vice president and cashier of NS&T, described the incident last night as "very unusual." He declined to comment further on the advice of the bank's lawyers, and indicated the matter was still under investigation.