A former District of Columbia government accounting officer was convicted last night of misappropriating $40,000 from the personal bank accounts of patients at Forest Haven, the city's institution for the retarded in Laurel.

The conviction of Lemuel L.Taylor, 39, followed a two-week jury trial in U.S. District Court in Baltimore.

In addition to being convicted on six counts of misappropriation involving the $40,000, Taylor was convicted of eight counts of theft in connection with a portion of the money.

The conviction covers offenses the government charged were committed between February 1979 and May 1980, when Taylor was acting chief of Forest Haven's field accounting office with duties that included administration of the funds. He resigned from his post at the 400-bed facility in June 1980.

During the period specified in the charges, Taylor made frequent trips to a bank in which the patients' accounts were kept and -- as one of only a handful of persons authorized to withdraw funds for them -- made frequent cash withdrawals, according to evidence presented at the trial.

Assistant U.S. Attorneys Ellen Hollander and Edward Norton contended that while Taylor gave some of the money to the residents, he kept substantial sums for himself.

Many Forest Haven residents, who range from children to the elderly, have accumulated sizable savings from earnings, inheritances and federal assistance payments.

Money taken from residents' bank accounts was supposed to be redeposited in a petty cash fund kept at Forest Haven so residents could buy specialized clothing, canteen goods and other items.

An investigation into allegations that thousands of dollars were missing from residents' accounts began in July 1980, after city officials received tips from a Forest Haven employe and a television reporter that were passed on by a Senate Appropriations Committee staff member.

At the time, James Buford, director of the Department of Human Services, which operates Forest Haven, acknowledged that safeguards on the accounts were inadequate, and said his department was moving to correct deficiencies.

In February, Taylor was indicted in connection with allegations of misappropriation and theft of $40,000. Subsequently, in a report to the mayor's office, D.C. Inspector General Joyce Blaylock estimated that a total of about $70,000 withdrawn from the accounts of patients could not be accounted for.

Federal prosecutors said last night that the investigation of Forest Haven was continuing, but gave no details.

The jury deliberated 15 hours and acquitted Taylor of two theft counts in the 16-count indictment.

The maximum sentence for misappropriation is five years; for theft, 15.