A D.C. Superior Court judge yesterday sentenced brothers Anthony and Clyde Stroman to a maximum of 27 years and 18 years in prison respectively for tricking a mentally handicapped man out of $3,500 he had inherited from his mother and for a related assault.

Judge Joseph M. Ryan, in handing down what prosecutors described as an unusually harsh sentence, told the two defendants that he found "particularly cowardly" their scheme to take the man's money on a promise to invest it in the city's illicit drug trade, adding that "society has a right to be protected from the likes of you."

Ryan sentenced Anthony Stroman, 23, to two terms of three to nine years for assault with a dangerous weapon in the incident and four terms of three to nine years for grand larceny.

Ryan ordered three of Anthony Stroman's prison terms to run consecutively and two concurrently. He suspended the sixth sentence and ordered Anthony Stroman to serve three years on probation after release from prison. Stroman must serve at least nine years before he becomes eligible for parole.

Ryan sentenced Clyde Stroman, 23, to two terms of three to nine years for assault with a dangerous weapon and two terms of three to nine years for grand larceny.

Two of the terms are to run consecutively, a third concurrently. Ryan suspended the fourth sentence, ordering Clyde Stroman to serve five years on probation after his release from prison. He will be eligible for parole after six years.

A jury convicted the Stromans after hearing testimony that they had bilked the money from Christopher Moore, 21, who was described in court as being at the second-grade level mentally and who inherited $13,000 after his mother's death in 1981.

Prosecutors said the brothers promised to invest Moore's money in the drug trade and share the profits with him. The assault charges stemmed from a threat the Stromans made against Moore's brother-in-law, who was investigating the use of Moore's money.

Moore had placed his inheritance in a savings account after receiving a check from his mother's insurance. 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 court testimony, 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.

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

Howard Berry, Moore's brother-in-law, testified that the Stromans threatened him with a shotgun after he attempted to question them about the bank transactions.

Both Stromans denied the charges.