Fred Dean -- the premier San Diego Charger defensive end, not the Redskin offensive line reserve of the same name -- has filed for membership in pro football's retired ranks, but Al (Bubba) Baker, the livin' end of the Detroit Lion defense, has reversed field and joined the Silverdome squad.

Baker was NFL defensive rookie of the year 1978. Dean was voted AFC defensive player of the year 1979 by his peers in the NFL Players Association. Both apparently are drawing, by current standards for athletes of their accomplishments, peanuts. Both went for long-term contracts before they established their stature, and neither Chargers nor Lions would accede to their demands for renegotiation before this season. So Dean never reported to camp and Baker left the Lions Aug. 5.

And now, Dean has written San Diego's front office: "It hurts me deeply to give this up, something I really love. I wish to play for the Chargers. When an employer won't discuss a grievance, there is nothing more a working man can do." He still could petition Commissioner Pete Rozelle for reinstatement.

Baker, who as recently as Tuesday demanded to be traded, ended his holdout after a meeting yesterday with General Manager Russ Thomas. So maybe Bubba finally won some concession from Thomas, who said, "Al and I agreed not to comment . . . We're just delighted to have him back in camp."

This could be the Lions' year, indeed . . .