Russell Davis, Pittsburgh Steelers running back from Woodbridge who was placed on the physically unable to perform list Monday because of a rare blood disorder, said yesterday that he may be able to play this season, depending on the results of tests he is scheduled to take in early August.

"All I know about this year," said Davis, who was voted "athlete of the decade" for the Woodbridge area in 1980 after lettering four years at the University of Michigan, "is that it's not completely out of the picture yet for me. I'm doing a lot of running and conditioning work, but I can't participate in any contact drills because I'm on steroids as part of the treatment. If I don't play this year, though, I'll play next year. I won't let this be the end for me."

Davis, the Steeler's fourth-round pick in 1979, said on the telephone that he first noticed "something just wasn't right inside" last year during a playoff game against the San Diego Chargers. He felt weak, queasy and had difficulty breathing.

He couldn't shake the cough that kept him up nights, nor could he shake the fear that "there was something really, really wrong with me." When a pain persisted deep in his chest, a pain that "felt like my lungs rubbing together," he turned to a friend for advice.

"My buddy told me I'd better check it out before it got too bad and possibly too late to do anything about it," he said. "I was scared then, real scared. I'd just bought a house in Pittsburgh for my wife and little girl and all of a sudden I was having these thoughts that somebody upstairs had played a trick on me. I kept saying, 'Why me? What did I do? Why me?' "

The day after Valentine's Day, Davis went to the doctor and underwent tests. He had just returned home when the phone rang.

"It was the doctor telling me to get to the hospital right away," said Davis, who has backed up Franco Harris at fullback for most of his pro career. Davis gained 72 yards on 24 carries last season.

"The doctors knew less about what was wrong with me than I did. At one point they thought I had pneumonia. But they wouldn't tell me that. They wouldn't tell me anything. Then I overheard the nurses saying I might have Hodgkin's disease. Nobody knew for sure and I began to feel like I'd been cheated, like I'd been singled out for some reason.

"There were a couple of mornings when I really broke down. I'd sit up in my hospital bed and cry. All I could think about was my wife and little girl. Football didn't seem important. It was secondary."

Doctors diagnosed Harris as having Boeck's carcoidosis, a blood disorder that afflicts mostly young black males. J.T. Thomas, a former Pittsburgh defensive back now with the Denver Broncos, sat out the entire 1978 season with the same disorder but returned to become a starter again in 1979.

"It's not only coincidental that J.T. and I both played on the same team and got this disease," said Harris, whose parents still live in the Woodbridge area. "He and I were both born in Georgia. For some reason most of the cases come out of the Carolina and Georgia area. But the doctors have no idea why . . . "

The Steelers team physicians were unavailable for comment yesterday.

Davis, who is undergoing steroid treatment for the disease, said, "I've got the typical moon face. I'm real uncomfortable because I retain a lot of body fluids but my attitude's good. At first I thought I'd never get the opportunity to play football again. But all that's changed. I'm optimistic. I'll be back."