A Prince George's police officer who fatally shot an unarmed burglary suspect in the back "has not committed a criminal act" and will not be tried by the state of Maryland, the county prosecutor's office has decided.

State's Attorney Arthur A. Marshall Jr. said he reached the decision not to seek an indictment of officer Lester J. Bethel after reviewing the evidence in the case. Bethel shot 18-year-old Abraham Dickens as Dickens exited the rear window of the Palmer Restaurant in Landover early on the morning of Jan. 21.

"In our opinion" Marshall wrote Police Chief John W. Rhodes, "Bethel has not committed a criminal act" under state law. "This by no means suggests that the actions of Officer Bethel were proper nor that other appropriate sanctions might not be imposed."

Bethel was placed on administrative leave following the shooting and still faces possible internal police charges, a departmental spokesman said yesterday. In addition, the incident is being investigated by the FBI for possible violations of U.S. statutes.

The fatal shooting of Dickens, who was back, by the 26-year-old white officer heightened racial tensions between police and citizens in the pre-dominantly black section of Prince George's County near the District line. Only weeks before, a black man suspected of shoplifting had been fatally shot by another white officer in the same district.

The county grand jury heard voluminous testimony in the earlier shooting before deciding not to indict Officer Peter F. Morgan, who still faces an administrative trial board.

In Bethel's case, the grand jury declined even to hear testimony after receiving the prosecutor's preliminary evaluation. In reaching its decision, the grand jury had Marshall's written statement that when the shooting occurred "it is clear that a felony was in progress, that Officer Bethel knew that the individual he confronted was, in fact, a felon in the act of committing a felony and further that the evidence, as known, could not contradict the suggestion that Mr. Dickens may have made a physical movement, consistent with Bethel's statement that he believed (Dickens) was reaching for a gun . . .

"I personally believe that, although a homicide was committed," Marshall said, "the homicide, based upon all evidence known at this time, was justified and would not support either an indictment or a conviction."

Marshall's conclusion was based in part on a memorandum from an assistant who noted that "while it would appear by hindsight that the officer could have safely delayed the employment of deadly force, it is my opinion that there is insufficient evidence to believe that an unlawful homicide has occurred."