D.C. police announced yesterday that they have made arrests in three recent homicides, including the murder of a 30-year-old counselor at a Northwest Washington group home for young offenders. Arrested in the counselor's fatal stabbing was a 17-year-old resident of the home.

Police also arrested an adult and a second juvenile in the murder last week of 86-year-old Rosezell Newman, a Southeast invalid who was shot in the chest, apparently by would-be robbers, as she lay in her bed.

In the third case, they arrested a man in the Oct. 24 killing of Jessie Carson, a security guard who was shot while he stood in front of a Northwest liquor store.

Police Chief Maurice T. Turner Jr. took the unusual step of calling a press conference to announce the arrests personally. He said he did so because some of the cases, particularly the killing of the elderly woman, had been widely publicized.

The body of the group home counselor, Russell Stanley Jr., of 1424 Kanawha St., Hyattsville, was found Oct. 27 in a vacant row house at 2827 15th St. NW. He had been stabbed repeatedly.

Stanley, according to police, had worked as a counselor at Try House, at 1459 Girard St. NW. Try House is one of 10 city-run group homes for youthful offenders. Turner would not release any details about the case yesterday other than to say that police had arrested a 17-year-old Try House resident in the killing.

The arrest came after a rash of recent assaults on counselors at the city's youth detention centers, and expressions of concern by city officials about problems of discipline and security in the institutions. Within the past four weeks, four staff members at Oak Hill and Cedar Knoll, the city's most secure juvenile detention facilities, have been assaulted. Three were hurt badly enough to require medical treatment.

In addition, a monthy discipline report for the institutions obtained by The Washington Post detailed continuing problems with escapes, minor fights, break-ins and drug use.

Youths at community-based facilities like Try House usually attend public or vocational schools during the week, and sometimes are allowed to visit their parents on weekends, officials said. According to Nancy McAllister, acting administrator of the city's Youth Services Administration, the homes try to create a "family-style" life for the youths.

Turner announced that in the case of the murder of the 86-year-old woman, police have arrested Franklin Lynn, 18, of 2513 Stanton Rd. SE, and charged him with homicide. Also arrested in the case was a 17-year-old male.

Rosezell Newman was asleep in her home at 1004 Howard Rd. SE on Nov. 3 when she was awakened by intruders. She was shot fatally in the chest, although she was an invalid who had suffered a broken hip less than two years ago, and was, in Turner's words, "no harm or threat to anyone."

In the case of the slain security guard, Turner announced, police arrested George Washington Precha, 38, of 1433 Monroe St. NW, and charged him with felony murder.

The 58-year-old guard, Carson, was shot to death during an attempted robbery as he stood in front of Astro Liquors, 3400 11th St. NW. Carson, who lived at 3512 New Hampshire Ave. NW, worked as a security guard with the MW Prince Hall Grand Lodge.