Fearing possible foul play, Prince George's County police asked the public for help yesterday in locating Diana Lynn Knack, a 22-year-old Forestville resident who disappeared Christmas Eve.

Knack, an employee for the past four years at the Giant Food warehouse in Landover, was last seen in front of her home at 6497 Pennsylvania Ave, by neighbors who watched her loading Christmas presents into a blue Plymouth Duster with racing stripes.

According to police, she was bound for her parents' home at 91 Herrington Dr., Kettering, that night but never arrived. The car she was driving is also missing, bears Maryland license tag "DTE 961" and is registered in the name of her father, Robert Lewis Knack.

After her parents reported her missing at 10 p.m. Dec. 24, state police began the search. The night of Dec. 26, a citizen found identification and credit cards belonging to Knack in the rear of the Tysons Corner shopping center in Virginia.

Police said that they had other reasons, aside from the discovery of the credit cards, to believe that Knack might have been harmed but they would not elaborate for fear of jeopardizing their investigation.

Police described the missing woman as 5-ft-8, 110 pounds, with brown eyes and shoulder-length hair. She is believed to have been wearing a camel-colored corduroy pants suit with tailored jacket and brown leather boots. She occasionally wears gold wire-rimmed glasses.

Anyone who may have information concerning Knack or her car is urged to contact the Prince George's police detective bureau at 336-8800, Extension 6691.