An Alexandria judge yesterday convicted Northern Virginia bingo operator James R. Fike of illegal gambling in a non-jury trial that marked the end of a year-long investigation of the city's $4 million yearly bingo industry.

Circuit Court Judge Donald Kent set sentencing for Fike for April 10.The felony carries a maximum penalty of 10 years in prison and $20,000 in fines.

Fike, who was one of the first people indicted last summer in the bingo probe, waived his right to a jury trial. The facts in the case were not in dispute, under an agreement between special prosecutor Edward J. White and Fike's attorney, James M. Lowe.

Fike was charged with conducting illegal bingo games in 1977 and 1978 through a firm named B & J Specialities. The same operation figures in the illegal gambling trial last month of Alexandria prosecutor William L. Cowhig. Cowhig was acquitted of the charge.

Lowe argued unsuccessfully that Fike, B & J's president was guilty only of violating the stste's bingo statute, a misdemeanor. White, who agreed to drop prosecution of a second illegal gambling count against Fike argued strenuously that B & J Specialties was not a charitable organization.

"This time they didn't even bother to grab a charitable front," White told the court. "Let's face it, B & J was a joke. It existed only to run bingo games."

Under Virginia law bingo games are legal only if sponsored by charitable organizations.

According to financial records introduced as evidence in court, the bingo games conducted by B&J Specialites grossed $43,700 in a six-month period.