An undercover police agent has charged in a sworn affidavit that a major bingo operator in Alexandria directed illegal games, boasted that he took "500 off the top" from profits, and falsified financial data to "mislead and defraud" Alexandria authorities and the charitable organizations for whom he ran the games.

On Friday police from Alexandria, Fairfax County, and the state of Virginia seized documents relating to the bingo operations from the home and office of Alva Ford Thompson, the man named in the affidavit as having run the illegal games.

The developments marked the first major action taken by special bingo prosecutor Edward J. White since he was appointed April 21 to investigate allegations of widespread irregularities in Alexandra's $1.2 million bingo industry. White released the affidavit yesterday.

No charges have been filed against Thompson, and no warrent has been issued for his arrest. "We are making an allegation against Thompson to support the granting of the warrant itself," White said yesterday.

The affidavit, sworn by Kathleen Bralove of the Alexandria police Department, also charged that Thompson instructed his employes to provide false information to Alexandria police. Specifically, the affidavit said, the employes were directed to say they were volunteers from the organizations listed as sponsors of the bingo games.

Virginia law regulating bingo games states that the games may be sponsored only by nonprofit or charitable organizations and that the persons running the games must be unpaid volunteers from the sponsoring group.

Thompson, reached at his home at 2303 Cavendish Dr. just south of Alaxandria, said he would have "no comment" on the allegations. He is the head of Metropolitan Talent Inc., which books bands and other entertainers for performances across the country.

The alleged by illegal games cited in the affidavit were conducted at a a bingo hall on Mount Vernon Avenue in Alexandria. That is the same hall where three bingo games for an Commonwealth's Attorney William L. Cowhig were held in May 1977. The games were stopped after officials at the Boy Scout national headquarters objected.

Because of his association with the Explorer troop and his involvement in getting $10,000 worth of bingo equipment for the hall from a Maryland firm, the commonwealth's attorney came under considerable pressure to step aside from the investigation in favor of a special prosecutor. Cowhig resisted at first, but finally acceded to the demand from Alexandria officials.

The affidavit stated that officer Bralove was employed by Thompson at the bingo parlor at 3819 Mount Vernon Ave. from April 13 to May 11, the day before the affidavit was filed. Bralove said Thompson controlled the bingo operations at the site in the name of Gridiron Inc., Arlandria Jackpots, TBA Auditorium, United Charities Inc. and other names.

Bralove said in the affidavit that she heard Thompson say, in a reference to the bingo games; "We have the winner take all every night, but no one wins it." In addition, Bralove said she observed Thompson "receiving and disbursing large amounts of currency while making entries in the books and accounts of various bingo operations."

The affidavit further charges that Thompson, through his company Gridiron Inc. received "exorbitant rents" for the parlor where the bingo games were held. Virginia law states that the rent charged to sponsors of the games for the halls must reflect fair market value prices.

The affidavit listed 33 groups that are possibly related to the operation of bingo games.

The records seized by the police at Thompson's home and at his office at 428 N. Washington St. included letters, ledgers, payroll records, invoices, daily sheets and other records of the bingo operations, bank statements canceled checks and leases.