An Alexandria printing contractor and an Energy Department printing specialist pleaded guilty in federal court yesterday to mail fraud and illegal gratuity charges growing out of an alleged scheme to steer government printing contracts to the Northern Virginia firm.

Prosecutors charged that during 1978 and 1979, Energy employe Eugene V. Davis awarded contracts worth $85,000 to Alexandria Graphics and Reproduction Services of 418 Hume Ave. The company was not the lowest bidder for the work, and Davis was employed part time by the firm, the government alleged. Davis pleaded guilty in U.S. District Court in Alexandria to one count of mail fraud and one count of receiving an illegal gratuity. Company president Earl R. Postell entered guilty pleas yesterday on the same two counts. Postell also pleaded guilty to a single count of filing a false income tax return for 1978. Prosecutors charged Postell understated his company's income by $57,000. District Judge Albert V. Bryan Jr. set sentencing for both men for Jan. 21. Davis, who has been suspended by the Energy Department, faces up to seven years in prison and $11,000 in fines. Postell could be sentenced to a total of 10 years' imprisonment and $16,000 in fines.