The Prince George's County Human Relations Commission has awarded $28,431 in back pay, its largest award ever, to a 44-year-old black woman from Suitland who was fired two years ago from a job at a Zayre's store.

Betty Roberts, a former security manager at the Zayre's store, 6256 Branch Ave., Temple Hills, alleged she was the victim of racial and sexual discrimination in connection with her firing on April 2, 1981.

Commission investigator Patricia Long said Roberts was fired after an area security manager discovered on an inspection that Roberts was allowing her 17-year-old daughter to fill in as an unpaid security officer when other employes went on break, a violation of company policy.

Although Robert's action violated company rules, Long said, the commission found that white male employes also had allowed their children to work as unpaid helpers at the store, assembling bicycles and bagging purchases, with the knowledge of company officials and without being fired. Long said Roberts' supervisers also knew she allowed her daughter to work at the store.

The Human Relations Commission, which received Roberts's complaint a week after the firing, awarded Roberts back pay and ordered that she be reinstated in her old job. Roberts had worked for the company for five years, making $5.14 an hour for a 48-hour week at the time she was fired.

Robert D. Harwick, a Baltimore lawyer who represented Zayre's before the commission, said the company is considering an appeal. He had no further comment.

Roberts said in an interview that she has searched unsuccessfully for another job since she was fired.

"You can't go look for another job when you've been fired," Roberts said. "You write down your resume and your application and everything and you have to say that you've been fired.

"I had four or five interviews, and they were all ready to give me the job and then they didn't want to take a chance on me. They said, 'Come back when you get situated with Zayre's.' "

Roberts said the company also tried to block her from collecting unemployment compensation, saying she had been fired for misconduct. But she received her money when a company representative failed to appear at a hearing called to appeal the decision.

Roberts said she hopes to return to her old job. "I'm really doing this for the people I left at Zayre's," she said. "I thought if I can do this, this will give the other employes the idea that they can, too."