Three persons were slain in separate incidents in the District of Columbia Monday night, bringing to 100 the number of homicides recorded by D.C. police in 1981.

In the first incident, Peggy Jean Washington, 32, of 1321 I St. NE, was shot in the chest during an argument at her home, police said. Washington was taken to Capitol Hill Hospital, where she was pronounced dead at 9:55 p.m. Police said a neighbor of Washington's, James Edward Jackson, of 1317 I St. NE, was arrested and charged with homicide.

Shortly before 10 p.m., Mary L. Price, 58, of 909 Monroe St. NW, was stabbed several times in an argument, police said. Price, whose home was set afire and partially damaged at the time, was taken to Washington Hospital Center, where she was pronounced dead shortly after 10, police said. Her nephew, Henry Steele Jr., of 1231 Madison St. NW, was arrested and charged with homicide in the case, according to police.

Police also said they found the body of Barney Lee Easton, 29, of no fixed address, at 11th and O streets NW at midnight. Easton, who had been shot once in the head, was pronounced dead at D.C. General Hospital. Investigation of the case is continuing, police said.

There were only 83 recorded killings at this time last year, police said.