An Alexandria Circuit judge has been asked to appoint a special prosecutor to investigate allegations that Commonwealth's Attorney William L. Cowhig solicited a sexual favor from a defendant's wife in exchange for a recommendation of leniency, sources said yesterday.

The request stemmed from allegations that details of the 1975 incident were covered up by local law enforcement officials, the sources said.

The woman, identified as Sherry Chenault, now of Baltimore, detailed the alleged incident in a sworn statement given to Acting Common-wealth's Attorney John E. Kloch yesterday, it was learned. Kloch also received taped conversations Chenault had with an Alexandria attorney, Gregory Murphy at the time, according to the sources.

Murphy, Kloch and assistant prosecutor Thomas Rawles Jones Jr., who handled the original case, met with Chief Circuit Court Judge Wiley Wright yesterday afternoon to make the request for a special prosecutor.

All four men refused to comment on the day's developments. Cowhig was unavailable for comment.

Cowhig, 53, was acquited twice of felony bribery and gambling charges connected to the city's bingo scandal in separate trials in the last two months. He faces a second felony charge of gambling in a trial now scheduled for March 5 in Alexandria Circuit Court. Cowhig has pleaded innocent to the charge.

All three charges have been handled by a special prosecutor, Edward J. White, who was appointed by now-retired Circuit Court Judge Franklin P. Backus last April 21. Cowhig was indicted last Aug. 3 and stepped aside from his office four days later pending the outcome of the charges.

According to sources, Chenault, now in her late 20s, and her husband, Daniel, had both been arrested in 1975 on drug charges. Sherry Chenault pleaded guilty and was placed on probation.

Before a jury trial for her husband took place, however, she was allegedly approached by Cowhig, who indicated to her that he would be willing to recommend a light sentence for her husband if they could "get together," sources said.

According to her statements at that time, Chenault accompanied Cowhig to his third floor office in City Hall where he asked her to commit oral sodomy. She said she performed the act. Sources said the incident occurred in the evening hours of a weekend day. They were alone in the office, according to the woman.

According to a source, Chenault later reported the incident to her husband's attorney, Roger Amole, now president of the Alexandria Bar Association, who allegedly informed the commonwealth attorney's office. Although Cowhig allegedly admitted to Amole and assistant prosecutor Jones that he had met with Chenault, he denied the sexual incident and later was administered a lie-detector test by the Alexandria Police Department, sources said.

The police department subsequently informed Jones that Cowhig had passed the polygraph test and the matter was dropped.

However, sources said, Alexandria prosecutors were informed by police officials in recent weeks that Cowhig told police before the polygraph test was given that the sex act, "with slight variation" in the details, had occurred. The results of the test, according to one source, were "misrepresented" to the commonwealth's attorney's office.

Cowhig did not recommend a light sentence for Danny Chenault, a source said yesterday. Chenault now is serving a jail sentece connected with a later drug conviction.

Sherry Chenault declined to comment yesterday through her attorney.

Sources said yesterday her allegations quietly resurfeace nine months ago during the Alexandria Police Department's investigation of Cowhig in connection with bingo-related charges. Kloch reportedly was informed several weeks ago.

Of the three police officials allegedly involved in the cover-up, two are presently on the force.

Former Police Chief John B. Holihan, who headed the force at the time, refused to comment last night on allegations of a cover-up.

Current Chief Charles T. Strobel also declined to answer a reporter's questions yesterday.

A source said yesterday that a decision on appointing a special prosecutor was unlikely before next Monday.

In a "Dear Bill' letter hand-delivered to Cowhig last Monday, Kloch, Jones and three other assistant prosecutors threatened a mass resignation if Cowhig resumed his official duties as head of the commonwealth's attorney's office. Two assistant prosecutors did not sign the letter.

Sources said last night that the charge against Cowhig and the alleged cover-up of the incident were the main reasons for Kloch's letter.

Also on Monday, Cowhig's long-time aide, Mary Ann (Sam) Pastorek, was placed on a 30-day administrative leave from the prosecutors' office. City officials refused to comment on the action.