Alexandria Commonwealth's Attorney William L. Cowhig requested yesterday that a special prosecutor take over from him the investigation of alleged improprieties in the operation of Alexandria's multimillion dollar-a-year bingo games, including an allegation that Cowhig himself was involved.

Cowhig returned last night from an out-of-town business conference and personally hand-delivered his unexpected request to Franklin P. Backus, senior judge of the Alexandria Circuit Court, Backus has authority to appoint the special prosecutor.

Cowhig, the official heretofore responsible for prosecuting any bingo violations, has said in the past that there is not enough evidence to prosecute anyone on charges of violating the state's bingo laws. These permit the operating of games only by volunteers to benefit charities in existence for at least two years.

Cowhig added in his letter to Judge Backus, that because allegations have been made about new irregularities, "the citizens of the city of Alexandria must therefore be left the impression that the bingo statute is not being properly enforced. Because public confidence in the criminal justice system is essential that situation is intolerable."

"I believe that I have become so (situated) with respect to this issue. . .as to render it improper in my opinion for me to act. That is the standard set out in the Virginia code for the appointment of a special prosecutor. Such an attorney would more clearly be able to determine objectively whether the evidence presented to him is a misdemeanor and whether the amount of evidence is sufficient to prosecute," Cowhig wrote.

"I want to clear the air concerning both the existence of possible illegality and the suggestion that I have acted in less than good faith," Cowhig wrote in his three-page letter to Jusge Backus.

Cowhig's letter is the most recent development in a month-long series of charges centering on bingo, the popular game that is the only form of gambling legal under Virginia law.

Although the legalization of bingo by the legislature in 1976 was meant to legitimatize the illegal games operated openly for years by churches, fraternal lodges and similar groups, its effect was to allow the development of huge games operating professionally in large halls.

In Alexandria three large-scale bingo games soon became popular. The biggest, organized by the Montessori School of Alexandria, took in $673,432 - not counting money used for prizes - and reported expenses of $386,369. This 43 per cent return of profits to charity is considered standard.

Other games, however, according to the reports they are required to file with the city, returned only 4 percent of their take to the charity the game was designed to benefit.

Later, The Washington Star reported that Cowhig had formed an Explorer Scout unit that listed three prosecutors in his office as adult members and that this troop conducted bingo games last May in allegedly technical violation of the law.

Cowhig, who has been in office since 1973, has consistently said that as commonwealth's attorney he does alleged violations of law, although he not have the personnel to investigate would prosecute if evidence were presented to him.

Cowhig had, until last night, refused to request a special prosecutor, saying he saw no conflict of interest between his law enforcement role and his relationship to the Explorer Scout troop.

City finance director Howard J. Holton said he has repeatedly sent to Cowhig's office information concerning unlicensed bingo games, principally conducted at a refurbished bingo hall on at 3819 Mount Vernon Ave., in the Del Ray section of the city. Cowhig has always declined to prosecute, saying the violaitons were either "technical" or "accidental" in nature.

Two weeks ago the Alexandria City Council sought to put a lid on smoldering dispute between city officials by the appointment of a city attorney and a official in the commonwealth attorney's office, to conduct a joint investigatin.

That situation exploded several days when it was alleged that David W. O'Brien, the representative from Cowhig's office, also was actually an officer of Cowhig's Explorer scout troop. O'Brien denied the allegations, and later resigned from the investigation.