As District police reconstructed it yesterday, John Clyde Foster, 42, was making his routine rounds as an employe of the Blackman's Development Center, helping criminal defendants gain release on bail.

He had been asked by the mother of a D.C. Jail inmate to bring her the keys to the inmate's Southeast Washington apartment, police said. Foster went to the jail on Dec. 15, and got the keys from inmate Clarence Thomas, police said.

Instead of turning them over to the mother, however, Foster used them to enter Thomas' apartment, police said, and removed $4,000 in property, including jewelry, clothing, stereo equipment and a 21-inch color television set.

Yesterday at 5 p.m., detectives arrested Foster at his own home, 2116 First St. NW, and charged him with second-degree burglary. Police also seized several items they said Foster had taken from Thomas' apartment in December and arrested Foster's landlord, identified as Nathaniel Walker, and charged him with receiving stolen goods.

In addition, detectives said they discovered several other items, including lamps, wall pictures and a TV set, taken from a Holiday Inn in Northeast Washington on Dec. 10. He has not been charged in that case, police said.

City authorities said a D.C. Superior Court grand jury is looking into broader allegations that a court liaison officer would extort money from defendants by threatening to report violations of terms of their release to court officials. Also, authorities said, the grand jury is investigating allegations that defendants paid money to a court liaison officer to "fix" their cases by stealing subpoenas from court records so that it would appear they did not have to show up for trial.

Police said Foster was also known as "Maj. Yahyah" an Islamic name typical of those used in the paramilitary black nationalist organization for which he worked.

Gen. Hassan Jeru-Ahmed, commander of the Blackman's Development Center, described Foster yesterday as a part-time court liaison officer who assisted in arranging "third party release" of Superior Court criminal defendants to Blackman's Development Center. The center, in an agreement with the court, supervises 300 to 400 defendants who are on bond awaiting trial, Hasson said.

Police said Foster was a key figure in Blackman's Development Center, but Hassan denied this. "He is not an executive officer in BDC," he said, "and has never been in a policy-making position."

Foster was convicted in February 1977 of mail and wire fraud in a major auto insurance fraud scheme and sentenced to 20 months to 5 years at the federal penitentiary in Petersburg, Va.

Later in 1977, Foster was released on a two-day Thanksgiving furlough but did not return to prison. A warrant charging him with prison escape was issued. In November 1978 a District police detective who had worked on Foster's original insurance fraud investigation, spotted Foster here working for Blackman's Development Center at Superior Court. Foster was arrested and returned to Petersburg. He was released in mid-1979.