An Alexandria man was convicted yesterday of operating an illegal bingo game at a parlor leased by Alva Ford Thompson, a promoter identified as a major figure in an investigation of illegal bingo operations in Northern Virginia.

The man, John Keator, was found guilty of running an illegal bingo game last February on behalf of the Bucknell Football and Basketball Association, inc. He was fined $100 by Fairfax County Judge G. William Hammer following a two-hour trial during which Keator's attorney, James Burkhardt, argued that his client had not run the game but was in charge only of the snack bar operation at the parlor.

Violation of the Virginia bingo laws is a misdemeanor and carries a maximum penalty of a $1,000 fine.

Thompson testified yesterday that he had telephoned Keator on Feb. 16 and told him that the Bucknell group would be issued a bingo permit by Alexandria finance dirctor Howard Holton for games at the parior leased by Thompson at 3819 Mount Vernon Ave. But Thompson denied that he had ever paid Keator for his services or that Keator had been one of his employes.

Holton and Charles R. Townsend of the Alexandria finance office both testified yesterday that a bingo permit had not been issued to the Bucknell group. The two men said that when they went to the bingo parior on Feb. 17 and found a game in progress, Keator admitted to them that he was in charge of the operation.

The testimony was denied by Burkhardt, who insisted that Keator was in charge not of the game but of the bingo parlor snack-bar. Under cross-examination by Burkhardt both Holton and Townsend admitted that they had not seen Keator call any numbers or sell any tickets for the game.

But Keator admitted from the witness stand that he had asked Holton if he wanted the bingo parlor closed and that in fact he had closed it after an-other bingo game had been played.

Keator is the second man convicted of a misdemeanor since an investigation was begun into Alexandria's $12 million-a-year bingo industry this spring.

Keator's attorney said he will appeal yesterday's decision to the Alexandria Circuit Court.

Thompson was arrested on June 1 and charged with a felony violation of Virginia's gambling laws in connection with alleged bingo irregularities.