Lewis R. Harris, Jr., 56, a retired D.C. police detective who later worked as a youth counselor and volunteer, died Thursday at the McGuire Veterans Medical Center in Richmond. He had a heart ailment.

Mr. Harris joined the Metropolitan Police Department in 1947 as a patrolman and was a detective when he retired in 1968.

He then worked as an aide and counselor in D.C. public schools until retiring a second time in 1975.

Mr. Harris was a volunteer with the Metropolitan Police Boys Club and worked with disadvantaged youth here. He served as general manager of the D.C. Sunday Softball League and was a founder of the Anacostia Satellites baseball team.

He was a native of Washington and attended Armstrong High School. He served in the Army during World War II.

Mr. Harris was a member of the National Association of Retired Policeman and chairman of the Fellowship of Retired Policeman and Firemen.

He attended Our Lady of Perpetual Help Catholic Church in Washington and was a member of the Knights of Saint John Post 286 and its bowling league.

He also was a member of the Pigskin Club, Sentinel Club, I.B.P.O.E. Lodge 1371, the Seafarers Yacht Club and the Arlington Divots Golf Club.

Survivors include his wife, Matilda M., of the home in Clinton; three daughters, Ramona Johnson, Patricia and Amelia, a son, Lewis, and an adopted son, Gustav Hamilton, his father, Lewis Sr., and a sister, Josephine H. Hinton, all of Washington and seven grandchildren.

The family suggest that expressions of sympathy be in the form of contributions to the Our Lady of Perpetual Help Church Building Fund, or to the D.C. Chapter of the American Heart Association. CAPTION: Picture, LEWIS R. HARRIS JR.