An unemployed construction worker was convicted yesterday of murdering a convenience store clerk in Fairfax County during a robbery attempt last spring.

James D. Fries, 19, pleaded guilty to the murder charge in Fairfax County Circuit Court after acknowledging that he shot and killed Franklin D. Sumter, 48, during the unsuccessful robbery of a 7-Eleven Food Store on Telegraph Road. Fries will be sentenced Jan. 8.

According to the evidence introduced by assistant commonwealth's attorney Steven A. Merril, the murder occurred about 2:30 a.m. April 21 when Fries and his accomplice, Bruce Walker, also of Fairfax, entered the store. Walker stood watch at the entrance while Fries went to the counter, leveled a sawed-off shotgun at Sumter and ordered him to hand over the money in the cash register.

Merril said Sumter accidentally pressed the wrong button on the cash register, causing it to emit a loud buzzing sound. Fries panicked, shot Sumter in the lower abdomen, ran with Walker through the front door and escaped without taking any money.

Fries was arrested by Fairfax police Sept. 9 after his girlfriend reported the incident to police. Walker was not charged in the Fairfax murder, Merril said, because he is being held in the District of Columbia in connection with other robbery charges.