District police, closing an investigation into the repeated intimidation of witnesses in a murder trial, arrested a 17-year-old juvenile yesterday and charged him with obstruction of justice.

The youth was arrested by members of the department's Special Operations Division at his home in Northeast Washington, authorities said.

Intimidation of witnesses, a persistent concern among law enforcement officials, led to the execution slayings last year of at least three people who were scheduled to testify in court.

Yesterday's arrests, Police Chief Isaac Fulwood Jr. said, emphasized the department's commitment to "protect the rights and safety of those citizens willing to step forward to help police . . . . "

The arrest culminated an investigation begun by District homicide detectives Louis Greene and Michael Sullivan, both assigned to the March 1990 deaths of two men found slain in an apartment near Barry Farms in Southeast Washington.

The victims, Fedor Diaz Sotolongo, 39, and Angel Santos, 28, were found in an apartment in the 2600 block of Birney Place SE. The two were targets of a robbery by two men and a juvenile who burst into the apartment and demanded money, police documents said. No drugs were found at the scene, but investigators said the slayings appeared to be drug-related.

Santos and Sotolongo, who lived in the apartment, were forced to lie on the floor and were then shot, police records show. Investigators subsequently arrested three people, including a juvenile, and charged them with first-degree murder.

The prosecution of the three suspects, all of whom were recently tried and convicted, was jeopardized when witnesses who had agreed to testify could not be located, or their willingness "dwindled," police said.

The targets of the threats were all women, and a separate investigation by Greene and Sullivan led to the arrest of the 17-year-old yesterday. Police did not specify the nature of the threats or say how many witnesses were involved.

Detailed information on the court cases was unavailable late yesterday.

Police identified the three suspects convicted in the murder trials, the last one in January, as Brian K. Williams, 18, of the 2600 block of Pomeroy Road SE; Robert Price, 20, of the 3700 block of Martin Luther King Avenue SE; and Kenneth Lampkins, 17, of the 4300 block of Vermillion Avenue in Oxon Hill.