Police in Prince George's County and the District arrested two 17-year-old youths Thursday night and charged them as adults with first-degree murder in the death of Patty L. Alston, the 19-year-old Capitol Heights woman found dead Thursday morning behind a District Heights junior high school.

Alston was killed one day before she was to testify as a key witness in an armed robbery trial, circuit court officials in Upper Marlboro said, and the case has been dropped.

Investigators said, however, that they could not make a positive link between the trial and Alston's death.

Interviews with Alston's relatives and friends led Prince George's homicide detectives to arrest Gustavous Otto (Fuzzy) Brooks, who lives in the 3100 block of Lassie Avenue in Suitland.

Brooks is being held in the county detention center in Upper Marlboro without bond.

County police also had a warrant for Brooks' cousin, Sylvester Lee Brooks, of the 1700 block of S Street SE, and D.C. police arrested Sylvester Brooks later on Thursday.

He is being held at the D.C. jail pending extradition to Maryland.

Alston's body was found by a student early Thursday morning in a playing field in the rear of Walker Mill Junior High School.

An autopsy by the state medical examiner in Baltimore revealed that Alston died of injuries received when she was struck and run over by a car.

Alston, the mother of an infant son, lived at 915 Brooke Rd. in Capitol Heights with her mother and brother, police said.

She was a senior at Suitland High School as was Gustavous Brooks, police said.

Alston was to have been the star witness in the armed robbery trial of Eddie M. Shackleford that was to have begun yesterday morning, according to county prosecutor R. William Hale.

Hale said that Alston had been working at the Rustler's Steak House on Silver Hill Road in Suitland on the night of Aug. 8, 1981, when the restaurant's manager was robbed.

Alston was the only person who could positively identify Shackleford and another man who had come into the restaurant together the night of the robbery, Hale said.

Prosecutor Hale said that yesterday was the last day that Shackleford could be tried under the state's speedy trial law.

In the face of Alston's death and the lack of other witnesses, Hale said that the case against Shackleford was dropped. Shackleford is serving a 12-to-36 year sentence in the District on other robbery charges, he added.