In April, when the Redskins traded for Joe Washington to strengthen their backfield, they weren't sure Terry Metcalf was good enough to sign as a free agent from Canada. And they certainly weren't counting on John Riggins to be in uniform for the start of the season, much less the beginning of training camp.

Now, less than a month before the opening game against Dallas, Riggins is not only back, but appears to be rounding into the same form he displayed two years ago, his best in nine pro seasons.

And Metcalf, driven by reports he no longer could play, is looking so good that he is rekindling ghosts of his St. Louis Cardinal past while projecting himself into game time that might have gone solely to Washington.

Toss in the third-down talents of Clarence Harmon, whose quickness seems to improve every year, and the steadiness of Wilbur Jackson, who was obtained a year ago to make the fans forget about Riggins, and the once-dismal Redskin running back situation instead has become one of the club's brightest spots.

Indeed, the problem now is how best to use all these players to the team's advantage. "It's something we are still working on," Don Breaux, backfield coach, said today. "We've got the basic personality and foundation of the offense established. But of the 15 running plays we might use in a game, we haven't got a finger yet on what ones we will emphasize to best utilize our personnel.

"We have a lot of good players with a lot of different skills. Every day we are getting a better handle on who should do what. We don't want to waste anyone. I think you will see two or three of them play a lot, especially on the early downs, and the other two or three be utilized frequently in specialty situations."

Although injuries and a sudden dropoff in progress by one of the veterans could alter things, the realization of what these backs are capable of doing has created an aura of excitement among the Redskin coaching staff.

So far, everything has worked out beyond Coach Joe Gibbs' fondest dreams. Joe Washington is adapting steadily to Gibbs' system while continuing to display the quickness that attracted the Redskins in the first place. Riggins, instead of sulking about his long-standing grievance against the team (in actuality, he is suing his employers while still playing for the them) has practiced like a man determined not to fail, even though the Redskins had shown their displeasure with him by trying to trade him off during the winter. And Metcalf has outworked all of his teammates in his push to show he has maintained the ability that had made him one of the league's most feared backs.

Metcalf's development has become icing on this backfield cake. No other NFL team really wanted him, and the Redskins were prepared to pass him by, only to have Gibbs insist on signing him. If Metcalf failed, it would cost Washington a fifth-round draft choice -- not a heavy price, but substantial enough for a club with too few picks in the first place. Within the organization, there was a feeling he might hang on as a sixth back, an insurance man in case of injury.

Instead of failing, however, Metcalf reported to camp with the rookies in superb physical condition and has climbed the ladder until he has emerged at a rung just below that of Washington. Against Kansas City Friday night, Metcalf came close to breaking two runs behind an offensive line still trying to get settled.

"I have every reason to believe that, by the first game, Terry will have established clearly that he is all the way back, that he is a legitimate NFL back again, like he was in St. Louis," Breaux said.

The Metcalf of Cardinal days, driven even then by barbs that said he was too small for the league, was a two-time Pro Bowler who was the first NFL player to ever account for 2,000 combined yards (rushing, receiving, returning) in three different seasons. The Metcalf of those days once gained 816 yards in a season and caught 50 passes in another.

Probably the only person not surprised by his current showing is Metcalf. He maintained from the start of his talks with the Redskins that he hadn't lost that much quickness, that he still was capable of being a quality running back.

To prove it, he even agreed to undergo a series of scouting tests usually reserved for college prospects. And he had so much faith in his ability that he also agreed to a contract loaded with performance incentives but lower in base salary than he normally would have accepted.

With Riggins (best marks: 1,153 yards, 36 catches) supplying the inside, short-yardage punch the Redskins missed last year and with Washington (best marks: 956 yards, 82 catches) and Metcalf adding much-needed quickness, Gibbs now has to solidify the offensive line to ensure they receive adequate blocking.

"But remember, good runners can make a line good," Breaux said. "They can do things to help blockers. The way our line is coming along, I don't see why this shouldn't all fit together."

Gibbs also will use the rest of the preseason to decide how to best employ his backs. The Redskins would like to have two established starters (most likely Washington and Riggins, both former No. 1 choices) and then work in the other backs. Metcalf and Harmon (best marks: 484 yards, 54 catches) probably will receive most of their time in passing situations while Jackson (792 yards, 53 catches) will spell Riggins and also team with him in short-yardage situations. But a pairing of Washington and Metcalf, with one cast as a wide receiver, wouldn't be surprising, especially if injuries cut into the squad.

And, finally, Gibbs has to decide whether he wants to keep a sixth back. Still in contention for that last spot are Bobby Hammond, Rickey Claitt, Ike Forte, Otis Wonsley and George Ragsdale.

"Performance on the special teams will help determine who the sixth guy will be, if we keep six," Breaux said. "It would be hard to play six during a game otherwise."

Right now, just trying to sort out roles for five backs is proving trouble enough.

Coach Joe Gibbs said today he hoped to be able to give quarterback Mike Rae, the veteran free agent signed two weeks ago, some playing time in Friday's exhibition game against Minnesota in RFK Stadium.

"Joe Theismann will start, and then Tom Flick will play, but I also would like to work in Mike," Gibbs said. He had considered using Rae in the preseason opener against Kansas City, but decided Rae wasn't familiar enough with the offense.

Rae, Theismann and Flick are receiving almost all the practice time at quarterback. Rae, as expected, has moved in ahead of rookie Phil Kessel.

Gibbs indicated that Mike Nelms and Terry Metcalf would return kicks in the game, along with Virgil Seay, who almost broke a kickoff return for a touchdown against Kansas City.

Coy Bacon has a sore knee and missed the morning workout. He returned for the afternoon practice, which was shortened again by heavy rain . . . Lemar Parrish was sidelined for the day with an upset stomach . . . The Redskins aren't actively pursuing another backup tight end, although General Manager Bobby Beathard apparently had considered Ruben Gant of Buffalo. But Beathard will watch the waiver lists closely . . . The Redskin workout Wednesday night will be a dress rehearsal for the Friday game . . . This morning's practice was one of the longest of the camp. Gibbs drilled the team at length on its running offense and defense, two of the early camp weaknesses . . . Gibbs hopes defensive end Mat Mendenhall will be able to resume practice next week. Mendenhall has been sidelined most of camp with a bad knee, but was jogging some today.