Prince George's County homicide detectives said yesterday that a body found in a wooded area in Cottage City was that of 22-year-old Joanne Nancy Grossnickle of Silver Spring, who had been missing since Labor Day.

Police said the victim, found Sunday, was fully clothed and appeared to have been stabbed to death. A formal autopsy report from the state medical examiner in Baltimore is expected today. The medical examiners' office used dental records to identify Grossnickle's body.

Police found the body about 6:30 p.m. after a man reported seeing it while he was collecting rocks near railroad tracks in an industrial area. Mount Rainier police Sgt. Jack Clements said the body was in some underbrush near the tracks far to the rear of the 3400 block of Bladensburg Road.

Grossnickle, of 1110 Fidler Lane, drove away from her parents home in Union Bridge, Md., in a new 1984 Nissan Sentra about 3 p.m. on Labor Day, relatives told police. She was reported missing when she failed to show up for work on Tuesday.

On Saturday, District police picked up two men driving Grossnickle's car. They arrested Rubin Jackson, 39, of 1327 Pennsylvania Ave. SE and Charlie Perry, 20, of 3549 Minnesota Ave. SE. Both were charged with unauthorized use of a vehicle. Perry was released on $5,000 bond; Jackson was held on a fugitive warrant from Montgomery County charging him with burglary. Police found belongings from Grossnickle's apartment in the car and in the apartment where one of the men lived.

Police sources said Grossnickle's parents, Byron and Virginia Grossnickle, visited their daughter's apartment several times last week and told police that pots, pans, a stereo and a couch were missing from the apartment.

Over the weekend, Montgomery County police determined that the Silver Spring apartment had been burglarized four times in four days without forced entry.

Grossnickle, a recent graduate of Towson State College, worked as the office manager for the Washington office of the Church of the Brethren. According to her family, she acted as a liaison between special interest groups and legislators on civil and human rights issues.

"To imagine the horrors she went through brings one to tears," Jay Arnold, a family friend, said yesterday. Arnold said the family had learned early in the day that the body might be Grossnickle's.