Washington Redskins rookie running back Timmy Smith, the team's leading preseason rusher, will start for the first time Saturday night against the Los Angeles Rams, running backs coach Don Breaux said yesterday.

The Redskins still are hoping George Rogers, who reinjured his sprained left big toe last Saturday and is not practicing, can start in the regular season opener Sept. 13 against the Philadelphia Eagles, Breaux said. But they also want to see how Smith, their fifth-round draft choice from Texas Tech, deals with the pressure of a starting situation.

"They want to see if I can handle it," Smith said after practice at Redskin Park, where he ran with the first-team offense. "I think I can handle it. I know George will be back and then I'll be booted back down, but this week I'll get a chance and I just have to go in and perform like I have been performing."

A second new starter on offense was revealed yesterday. Glenn Dennison, a Redskin for less than two weeks, will start in Clint Didier's place at H-back against the Rams. Didier has a pulled left hamstring and is expected to be out several weeks.

Dennison, acquired in a trade with New England, was the second-round draft choice of the New York Jets in 1984. A standout tight end on the University of Miami's 1983 national championship team, Dennison started nine games for the Jets in 1984, catching 16 passes for 141 yards. He suffered a back injury and missed the entire 1985 season, then was released and signed by the Patriots.

Coach Joe Gibbs said Dennison picked up much of the Redskins offense very quickly and sparkled in the Tampa Bay game, making "about three or four" good blocks immediately. Dennison also is a good special teams player, Gibbs said.

"I don't think anybody who comes in that late will know {the position} the way you want them to, but he's really a bright guy," Gibbs said.

"It's not a scary thing," Dennison said. "It's not as if I'm not practicing all week. I'm working with the first crew. I feel comfortable, and I think I'll feel more comfortable by the end of the week."

Rookie free agent H-back Craig McEwen of Utah will share playing time with Dennison in the game at Anaheim Stadium (9 p.m. EDT), Gibbs said. McEwen is the leading candidate for the Redskins' second spot at H-back due to the unexpectedly severe nature of Terry Orr's bruised left shoulder.

"He's an extremely good pass receiver," Gibbs said of McEwen. "I want to see him block this week."

McEwen is 6 feet 1 and 220 pounds; Dennison is 6-3, 225, and Didier is 6-5, 240.

When asked about this size differential, especially for McEwen, tight end coach Rennie Simmons said, "As long as they keep performing, they've got a chance."

To reach the required 60-man roster limit, the Redskins placed veteran tight end Anthony Jones on the physically unable to perform list and placed four rookies on injured reserve: tight end Alfred Jenkins, the team's ninth-round draft choice; center Ray Hitchcock, the 12th-round pick; free agent defensive tackle Chris Spachman, and free agent running back Greg Grooms.

Jones, who suffered a severe knee injury last December at Denver and underwent surgery, is expected to miss most, if not all, of the season.

Of the 60 players on the roster, 48 are veterans and 12 are rookies and first-year players. The Redskins must cut down to 45 players by next Monday.

Injuries, personality quirks and playing time have made running back one of the team's most intriguing positions this preseason. Kelvin Bryant, who wondered aloud why he was not running the ball last Saturday night, followed Smith onto the field and ran the ball a half dozen times yesterday in practice.

"I liked that," said Bryant, who missed two weeks with a strained right quadriceps. "I'd like to run the ball more. That felt good."

"What we've hoped to do is give him some run work," Gibbs said. "Last week, we were just hoping to get him in the game, catching and feeling good . . . Hopefully now he'll be ready to carry some this week."

The odd man out of the running back picture, at least for the moment, is Keith Griffin. He started the first two preseason games but was used sparingly yesterday in practice.

"In a way, I'm disappointed," he said. "I guess they want to see what Timmy can do at the beginning of the game. That's what they want to do, so I've just got to go along with it."

Smith, 5-11, 216 pounds, has carried 46 times for 177 yards in three preseason games for a 3.8-yard average. He has scored two touchdowns, one on a 33-yard run at Tampa Bay. It's safe to say he has been the Redskins' most impressive running back this summer, and has been all the Redskins had hoped he would be when they drafted him in April.

Redskins Notes:

In addition to Rogers, Didier, middle linebacker Neal Olkewicz (knee) and defensive end Dexter Manley (knee), starters who did not practice yesterday were defensive tackle Dave Butz and cornerback Tim Morrison, both with bruised calf muscles . . . Gibbs reiterated that veteran Curtis Jordan and second-year player Todd Bowles are locked in a fierce battle at free safety. Jordan still is practicing with the first team . . . The Redskins added a new twist to their center-exchange practice. Quarterback Mark Rypien soaked the football in a bucket of water before handing it to center Russ Grimm or Jeff Bostic, who then snapped it to Jay Schroeder or Doug Williams. The object was to simulate the wet conditions that gave the Redskins trouble at Tampa Bay, when Schroeder and Rypien each fumbled a snap.