Late last Sunday, fullback John Riggins of the Washington Redskins sat slumped in a locker room chair. He had just added 27 carries against St. Louis to the 2,713 he had logged against the National Football League at large. His head was shaking and his back, it seemed, was creaking.

Riggins said at the time he expected that, by late this week, he would be forced into Sibley Memorial Hospital for a third time this season to get rest and traction for his lower-back pains and for the bursitis in his hips.

"I'm going to wait to see if I have a relapse," Riggins said, "which I anticipate that I will."

At 35, Riggins is the league's oldest running back. Although he is in the final year of his contract, he said he will wait until the offseason to decide if next year will be his 14th of playing professional football or his first in retirement.

"If I know that next year will be like this year," said Riggins, who this season ran for 1,239 yards, the second-highest total of his career, "I wouldn't go through with it again."

Riggins did not require hospital time this past week, after all. "He came in for his workout (Thursday). His back feels good," trainer Bubba Tyer said, "and his legs feel good, too. He looks good."

Nevertheless, the Redskins' master planners are planning for the future as if Riggins won't be around. Just to be safe.

"We'll wait till the dust settles in the offseason and see what John decides," Coach Joe Gibbs said, "and we'll see how Joe (Washington, veteran running back) feels, too. But this year, we know that we want to get a good, young running back."

General Manager Bobby Beathard has made the running back position his No. 1 priority. Washington, 31, has had only 56 carries this season because of the umpteenth knee injury of his career; rookie Keith Griffin has tarnished his best moments of slash and dash (408 yards) by fumbling too often (a team-high eight). Furthermore, Griffin earned a roster spot primarily as a pass catcher, but has caught just eight passes.

Running backs Jeff Moore (17 catches) and Otis Wonsley (a short-yardage/goal-line blocking back and special teams leader) are role players, not suited for full-time play in the one-back offense.

Even though Gibbs insists that his offense changes as much as "30 to 40 percent a year" and he speaks of someday changing to a three-back offense, he still seems committed to the concept of the one-back offense.

That commitment makes the Redskins' push to acquire a running back even more vital. "We're just looking for a real good runner, a threatening-type back," General Manager Bobby Beathard said from Montgomery, Ala., where he spent all week scouting players in the Blue-Gray college all-star game.

Florida State's Greg Allen and Kentucky's George Adams are among the most respected runners eligible for this year's draft. "No, it's not a real good stock of (college) running backs this year. I'd say it's above average, but not a top year," Beathard said. "I'd say we're just going to have to pick two or three running backs out of that and hope that we can get one of them.

"And then," Beathard said, "we'll also talk to every (NFL) team that might have a running back available."

A trade seems to be the Redskins' most likely way to acquire a quality running back. Last offseason, Beathard spoke with Houston to see if Earl Campbell, a three-time league most valuable player (1978-80), might be available. When Ladd Herzeg, Houston's general manager, said the Oilers might consider a deal if the Redskins' all-pro left tackle, Joe Jacoby, were included, Beathard backed off.

Six weeks into this season, Campbell was traded to New Orleans. Now, it seems that Campbell finally has fallen victim to seven seasons of trying to knock over linebackers rather than trying to elude them. He doesn't seem to move as fast or with the same confidence, NFL scouts say. Campbell gained only 190 yards on 50 carries and did not score any touchdowns.

One running back who seems perfectly suited for the Redskins' needs is Kelvin Bryant, selected in the seventh round of the 1983 draft by the Redskins. But he signed with the Philadelphia Stars, became the U.S. Football League's best ball carrier and still is the property of the now Baltimore Stars.

Beathard said it is unlikely the Redskins will sign Bryant, at least in the near future. "He's got three years left on his contract (with the Stars). To be truthful, we've never even thought of him. We've never pursued that. (Signing with the Stars) was a decision that the guy made or a decision that was made for him. We were never even in it," Beathard said.

It doesn't help Beathard that the Redskins no longer possess their picks in the third, fourth and fifth rounds of the 1985 draft. Beathard swapped those picks in trades to acquire center Rick Donnalley (fifth, to Pittsburgh), wide receiver Calvin Muhammad (fourth, to the Los Angeles Raiders) and the Redskins' third-round '85 pick for the Oilers' fourth-round pick in 1984. Beathard used that fourth-round choice to select since-released running back Jimmy Smith.

"We'll look into the possibility of making a trade, although whether we make one will depend on what kind of draft choices we'd have to pay," Beathard said. "We'll wait until the playoffs are over. We'll sit down and talk about it with our staff."