A D.C. Superior Court judge, in a highly unusual development, said yesterday he will order the release of three men in jail awaiting trial on felony charges because their trial dates conflict with that of a fourth man he ordered detained.

Judge Timothy C. Murphy announced his decision, which law enforcement sources said was unprecedented, after prosecutors asked him to hold Lenard E. Green, charged with robbery, contempt and obstruction of justice, under the District's preventive detention law.

Conditions of that law require that defendants be brought to trial within 30 days. Murphy said in his order granting the government's request that holding Green on preventive detention will mean continuing seven other cases on his trial calendar.

Murphy said he will release three of the persons being held in those cases when their trial dates come up in early February. All three have spent months in prison awaiting trial.

"This is not a new problem," Murphy said in an interview yesterday. "There is a terrible dysfunction in the system, and it's a function of priorities. If the government's priority is going to be to hold him Green , then that's fine. But if I can't reach the other three because I have to try him, then I'm going to let them out." He said he will explore the possibility of giving their cases to another judge, but that judges are "generally not available."

One of those Murphy has slated for release is Reginald Jackson, who has been awaiting trial for 14 months on two counts of sodomy and two counts of taking indecent liberties with minor children in January 1981.

Jackson was indicted on those charges Dec. 9, 1981, and a trial date was set for June 21, 1982. Neither prosecutors nor Jackson's attorney could explain yesterday why his trial has been delayed.

Another of the men Murphy selected is William A. Reeder Jr. According to Murphy, Reeder has been held 16 months awaiting trial. He is charged with robbery and failing to make a court appearance.

The third man, Cleveland Burgess, has been held seven months, Murphy said. Burgess is charged with heroin and cocaine violations.