A D.C. Superior Court jury yesterday convicted two brothers of grand larceny for their involvement in a scheme to trick a mentally handicapped man out of part of his inheritance by promising to invest his money in the city's illicit drug trade.

Anthony Stroman, 22, and Clyde Stroman, 24, were each convicted on counts of grand larceny by trick and assault with a deadly weapon. Anthony Stroman faces a maximum 60 years in prison as a result of the conviction, his brother a maximum of 40 years.

The Stromans were accused of taking money from Christopher Moore, a mentally handicapped 21-year-old who had inherited $13,000 after his mother's death in November 1981. Prosecutors said the two promised to invest Moore's money in the drug trade and share the profits with him. The assault charge stemmed from a threat the Stromans allegedly made against Moore's brother-in-law, who was investigating the use of Moore's money.

Moore, who was at the second-grade level in school according to court testimony, had placed his inheritance in a savings account after receiving a check from his mother's insurance last year.

Under questioning from Assistant U.S. Attorney Kathleen E. Voelker, he testified that shortly after he received the check, Anthony Stroman, whom he had known since grammar school, proposed using $4,000 of the money to buy and sell drugs. According to testimony in court, within a three-day period Moore gave the Stromans $3,500 after the Stromans wrote out withdrawal slips and Moore copied them and took them to the bank.

Howard Berry, Moore's brother-in-law, testified that after learning of the first withdrawal of $1,000 he tried to stop any further transactions by taking Moore's bank identification, but that Moore continued to make withdrawals.

Berry testified that the Stromans threatened him with a shotgun when he attempted to question them about the bank transactions.

Prosecutors said there was no question in the case of a conspiracy to buy and sell drugs because prosecutors believed the Stromans intended to deceive Moore and not to engage in drug trafficking. The Stromans had denied the charges.

Judge Joseph M. F. Ryan Jr. set sentencing for Feb. 18.