A D.C. police officer who was suspended from the force in 1972 after being charged with an armed robbery of which he was acquitted, was convicted by a Prince George's County jury yesterday of possessing three ounces of marijuana and transporting a handgun in an incident last fall.

The officer, Willis Thomas Poole, 32. of Suitland, was dismissed from the D.C. force by a police trial board in March 1976 but was ordered reinstated last month by a U.S. Civil Service Commission appeals board.

Members of the D.C. police internal affairs office were present at Poole's trial yesterday but refused to comment on what effect the verdict might have on his reinstatement.

The Circuit Court jury that convicted Poole yesterday also acquitted him of a charge of assaulting a 20-year-old Forestville woman before his arrest last Sept. 20.

Poole could receive up to a year in jail on the marijuana charge and three years on the weapon conviction, according to Assistant State's Attorney Gary A. Courtois. Sentencing is scheduled for Aug. 30.

Poole's attorney, Robert Silberman, said Poole plans to appeal the convictions on constitutional grounds. Poole refused to comment.

The same appeals board that had ordered Poole's reinstatement had ruled he must be paid for the period between March 1976 and January 1977. According to Silberman, Poole planned to pick up a check for the back salary today.

Poole, who joined the D.C. police force in 1968, was arrested on a charge of committing an armed robbery in March 1972 while off duty. He was acquitted in July of that year.

The incident that lead to Poole's arrest last September began when a towing company was called to the City Lane Towers at 3901 Suitland Rd., where Poole lived, to remove his car from a fire lane, prosecutor Courtois said.

Poole arrived as the two truck prepared to pull away, and became abusive with the driver of the truck and his passenger, A Forestville woman, Courtois said.

Poole then pulled three package of marijuan from his car and handed them to a friend, who fled, according to Courtois.

The man was stopped by a City Line security guard, who recovered the marijuana after a struggle during which the man escaped, Courtois said.

Poole was arrested by Prince George's County police. After impounding his car, police discovered a .25 baliber handgun in the trunk, Courtois said. He added that because Poole was a suspended police officer, he was not licensed to carry the gun.

Poole also was arrested last Friday on a disorderly conduct charge at the Hyatt Regency Hotel, 400 New Jersey Ave. NW, police said.