Bill Austin was coaching the Redskins when the Dallas Cowboys last had a rookie starting in their secondary. Cliff Harris, a free agent, broke in as the regular free safety in 1970 and now, 11 years later, another free agent will be under fire Sunday at RFK Stadium.

Mike Downs, 6 feet 3, 195 pounds from Rice, has surfaced from all the disarray in the Cowboy secondary and will be the free safety in the season opener against the Redskins.

When Randy Hughes suffered another shoulder separation two weeks ago, Dennis Thurman was shifted from free safety to left cornerback opposite Steve Wilson, a former Howard University star at wide receiver, and Downs moved into Thurman's spot.

The most remarkable aspect of this rare success story in Dallas, however, starts much earlier, back when Coach Tom Landry invited several anonymous free agents to his summer camp in Thousand Oaks, Calif. Not even this wise and experienced coach could have foreseen that one of them would be in his starting lineup on opening day.

"I never expected this to happen," Downs said yesterday. "When I didn't get drafted, I hardly expected to make any team this year, let alone the Cowboys."

Although he played four seasons at safety in the pass-happy Southwest Conference, although he worked out for several scouts, although his size and speed definitely were pro caliber, Downs was disappointed on draft day.

"After working out for several teams, a lot of people told me I would get drafted in the middle rounds," he said. "A couple of teams contacted me after the draft, but there was nothing definite. I talked with Pittsburgh, but once the Cowboys called me, there wasn't any choice. I've always been a Cowboy fan.

"I really didn't have any aspirations, though," he added. "Realistically, I knew the secondary was set. None of the veterans had retired."

As just another free agent, Downs made an interception and several impressive tackles in a rookie scrimmage against San Diego. On the strength of that performance, he survived the first major cut and therefore was in a position to get a chance when Hughes reinjured the shoulder that was separated twice last season.

"I saw a little bit of an opening," Downs said. "I figured that free safety is the only position (at which) a rookie could break in. There's just too much single coverage at cornerback."

Following two impressive performances as a reserve, Downs got his first start Aug. 22 against Pittsburgh, when Landry shfted Thurman to cornerback.

Thurman had played the corner his first two seasons before moving to safety when Hughes was sidelined last year. When he played well against the Steelers, it opened the door a little wider for Downs.

"I felt all along it was a day-to-day thing," he said. "Each day you survive, you know your chances are improving. That's what you need to keep going. Once I got a chance to start, I felt I could, at least, make the 45-man squad if I kept playing well."

Landry, asked if he were apprehensive about opening in Washington with a rookie, replied, "He's been very good all summer. If he hadn't been, we wouldn't have him back there."

Despite his inexperience, Downs doesn't feel he will be singled out Sunday as a special target by Joe Theismann.

"I don't think I'll be in a position to be picked on," he said. "It's not like I'm playing on a corner. It's hard to isolate a free safety."

Obviously, for the last rookie to break in at that spot for the Cowboys managed to survive nine seasons.