If Rich Milot were coaching the Detroit Lions this week, he is certain he would pick on the Redskins' rookie outside right linebacker.

"It's logical," said Milot, who happens to be that linebacker. "You test a rookie until he shows he can do the job. If he does, then you go another way. If he doesn't, you keep coming at him."

The same could be said for the entire Redskin rushing defense. Until the club proves it can stop the run this season, opponents are going to keep trying to jam it into the guts of the unit.

Detroit, Washington's opponent on Sunday, appears to have little choice but to stay on the ground. With a rookie quarterback, Jeff Komlo, getting his first pro start, the last thing the Redskins expect is a lot of passes. Besides, the Lions did quite smartly (231 yards) running aginst the Redskins last season.

For Milot, that probably means another busy afternoon trying to prove Coach Jack Pardee's belief that the rookie's presence makes Washington's rushing defense better than in 1978.

Pardee says that Milot, a 6-foot-4, 226-pound Penn State product, adds quickness, range and tackling ability to the spot, manned so ably for so many years by Chris Hamburger. The coach sees stardom in Milot's future, a pretty heady billing for a seventh-round draft choice who never had been plugged as another future Nittany Lion linebacking great.

Milot doesn't know what he sees at this point. The move upward has been so swift -- from not knowing if he would be drafted, to surviving the final squad cut to promotion to first string before the opening game -- that things are just starting to sink in.

"I feel more comfortable this week than last," he said yesterday. "I'm starting to better understand the position. You can play a better game when you know what is going on."

It is around such athletes as Milot that Pardee is trying to rebuild his defense. The gamble to go this early with both Milot and middle linebacker Don Hover may result in growing pains, as Earl Campbell and Houston showed Sunday, but the Redskins believe that with experience, the youngsters will tighten up the rushing leaks.

Until the two develop completely, Pardee also will use gimmicks. Last week, it was Kenny Houston playing a middle linebacker. This Sunday, it could be more 3-4 and possibly a move involving Ear Lorch replacing Joe Jones at left end and Coy Bacon moving to right end.

"I'm looking for Detroit to run and try bombs," said Pardee. "You can't have a young quarterback take five steps and heave it long. But it's the seven-step drop-back and timed passes that take years to perfect.

"It's logical for them to run. They ran on us last year and yes, we'll have to show we can stop the run before anyone will stop testing us. They don't have to have a rookie to try it on the ground against us."

Milot has spent this week studying the moves of Lion backs Horace King, Dexter Bussey, Lawrence Gaines and rookie Bo Robinson. Starters King and Bussey have drawn most of his attention, just as Campbell did last week.

"Funny, Houston really didn't run at me like I thought," said Milot. "I didn't think they tested me." But unlike the Oilers, who concentrate on the middle, the Lions are less narrowminded. Using angle blocking and a young front line, they pick and test every part of the defense, probing for weaknesses.

And while they experiment, Milot will be learning.

"I've got so much more to learn," he said. "So far to go. But it helps now being a starter. I might have prepared just the same before but by being on the field more (during practices) and working with Brad Dusek more, it's very helpful."

"This whole thing didn't surprise me completely, because I had a lot of playing time during preseason and they seemed satisfied with what I was doing. But I really never expected to be starting this quickly, if at all. There isn't enough time to think about it that much. It just happens."

Milot's gracefulness, his quickness (he can run a 4.7 40 on wet grass) and his angular build (resembling that of Steeler Jack Ham) make him eyecatching on the field. From early in camp, he started drawing Pardee's praise, as did another youngster, Monte Coleman, who may have even more natural ability.

These same characteristics attracted General Manager Bobby Beathard's attention during a scouting trip last year to Penn State. While others were watching more heralded athletes, Beathard remembers the thrill of viewing Milot.

"I got so excited that I kept hoping no one else noticed," said Beathard. "He stood out, he had everything that you want in a linebacker."

Except experience. Only during the last seven games of his senior year had he played "monster back" in Penn State's defense -- and that spot required the mixed skills of a linebacker and secondary man. Before then, he had dabbled at running back, receiver and defensive back.

Since Milot had played so many positions, yet did not specialize in any, his computer rankings were low. He was a man with talent who lacked identity, just the type the Redskins needed to locate in the sparse 1978 draft.

"We figured he would be around for awhile, but we also thought he had great natural ability," said Beathard. "You look at him and say, "Linebacker,' He can get stronger and bigger. There is no end to what he can do."

Whether Milot becomes another Ham or another washout has yet to be proven. After one game, he is anxious for more tests of pro football life, although he already talks with the confidence and sophistication of a veteran. The Lions are plagued with injuries. Beside losing two quarterbacks, defensive tackle Cleveland Elam (Hand), defensive back Tony Leonard (knee) and defensive back Walt Williams (knee) are out. Rookie tackle Keith Dorney is ailing and may not start . . . Pardee says he will continue to have tight ends Don Warren and Jean Fugett bring in plays. "Each does something better than the other.'" said Pardee . . . Last year, the wide receivers were play-carriers . . . Quarterback Joe Theismann is wearing one of those flak jackets first popularized by Houston's Dan Pastorini, but only as a preventive measure. Mul-Key Is Arrested

Former Redskin running back Herb Mul-Key was arrested yesterday morning at the Fort Totten subway station and charged with fare evasion, according to Metropolitan Transit Police.

Mul-Key, who could not be reached for comment, posted $25 collateral on the misdemeanor charge and is scheduled to appear in Superior Court Sept. 17. The fine for first-time fare evasion is $50.

According to a Metro spokesman, Mul-Key "insisted on going through the gate without the proper farecard." Mul-Key had a farecard, but it did not open the gate for unknown reasons, the spokesman said.

The spokesman added that he did not know if Mul-Key, now a computer salesman, had a card with insufficient fare or if there was something wrong with the card or fare machine.