U.S. Attorney General William French Smith has been asked to force federal prosecutors here to reveal the source of allegations that a District of Columbia deputy police chief improperly ordered the release of two robbery suspects.

The request came in a letter from the Washington Metropolitan Police Officials Association, acting on behalf of Deputy Chief Alphonso D. Gibson, who is angry over a month-long investigation of him by federal prosecutors.

The investigation, prompted by allegations that Gibson had released the two men because they were his relatives, concluded last month that he was in fact not related to the two men and had done nothing wrong.

But the fact that he was investigated at all has left Gibson steaming, and that has become the point of a squabble between representatives of two elements of the criminal justice system that are supposed to work as a team.

"Why didn't they just call me?" Gibson said recently. "I could have told them it wasn't true. It would have taken five minutes."

Gibson--commander of the criminal investigations division, which includes the homicide, robbery and sex-offense branches--now wants to know the name of his accuser, who he suspects is another policeman.

"It is against the law to falsely accuse a police official," Gibson said. "And when I find out who did it, I'm going to see he's disciplined, unless he can prove to me he didn't do it on purpose."

Stanley S. Harris, U.S. attorney for the District of Columbia, has declined to comment on the investigation. In a recent letter to Gibson, Harris said: "When information is conveyed to this office in confidence . . . the sources cannot be divulged."

Gibson brought his case to the association, which represents about 250 of the city's police officials, last month. After hearing him describe the investigation, members concluded that the handling of the allegations by federal prosecutors, rather than police investigators, represented "a threat to all officials of this department."

They subsequently voted to write Smith to ask, on Gibson's behalf, that Harris be forced to reveal to police officials the source of the allegations.

The group's letter, written by association president Inspector Max Krupo, expressed "complete shock and outrage at the insensitivities and irresponsible actions of some members of the U.S. attorney's office."

Justice spokesman Robert Stevenson said yesterday the association's letter has been routinely forwarded to the department's office of ethical responsibility and "will receive due consideration."

"We certainly don't want a war with the U.S. attorney's office," Krupo said yesterday. "What we would like is some sign of respect, that we're thought of a little more highly" by federal officials.

Knowledgeable law enforcement sources said the investigation of the allegations against Gibson was requested by Gibson's boss, Police Chief Maurice T. Turner. Turner declined to either confirm or deny initiating the probe, saying: "that is privileged communication between the U.S. attorney's office and myself."

Sources said Harris expects the letter to prompt a Justice Department inquiry into how, and why, the original investigation was undertaken.

Gibson's complaint stems from an incident last December in which two men were charged with being accessories in a robbery. Robbery squad officials subsequently dismissed the charges as unfounded. Gibson reviewed the case.

Prosecutors received allegations that the two men were related to Gibson and that he had improperly interfered in the case on their behalf. According to a knowledgeable source close to the prosecution, prosecutors pursued the matter because it appeared Gibson had taken what the source described as an "unusual personal interest in how the case was being handled."

Chief Turner, defending Gibson's action in the case, said that "the only thing he Gibson did was review administratively" the release forms.

On April 8, after the investigation was completed, Harris wrote Gibson that "there is no evidence whatsoever of any misconduct or wrongdoing on your part."