If Leonard Mitchell, the top-rated defensive lineman in the National Football League draft this month, is available when the Redskins pick in the first round, they apparently will not take him because he failed to report for a workout with team representatives last week in Houston.

Mitchell is an imposing 6-foot-7, 270-pounder, and the Redskins have an obvious need for an intimidating, pass-rushing defensive lineman. But team sources say they are too unsure of his work habits and dependability to risk the ninth selection in the draft on a player who may not become a star.

General Manager Bobby Beathard confirmed that Mitchell missed a scheduled tryout with a scout and assistant coach. That Beathard admitted, has given the team second thoughts about drafting the University of Houston defensive end.

"This is such an important choice that you have to be absolutely sure about it," he said. "We've had a lot of conflicting reports on him, about how hard he is working in the offseason. He can be such a dominating player in the NFL if he wants to be. He certainly has all the ability.

"If we did pass him, we would hate to have him drafted by anyone else in our division."

Washington had thought Mitchell would be taken long before its ninth pick came up. But sources indicate that Mitchell's rating around the league has been eroding to a point where he may last longer in the first round than expected. The draft will be held April 28 and 29.

Although the Redskins still are leaning toward drafting a defensive lineman in the first round, Beathard would not rule out selecting an offensive lineman, a running back or even a quarterback.

They also are continuing trade talks aimed at giving up their first-round pick for a lower first-round selection plus either a second- or a third-round choice.

"It's 50-50 that we will be able to make a trade," Beathard said. "We need a lot of players from the draft, so we are willing to be very flexible."

If Washington does draft a defensive lineman, the most likely candidates are Keith Gary, a 6-3, 260-pound end from Oklahoma; Donnell Thompson, a 6-4, 265-pound end from North Carolina, or John Harty, a 6-4, 266-pound tackle from Houston, are being considered.

In a recent national magazine article, Dick Steinberg, director of player development for New England and one of the most respected personnel men in the league, had Mitchell, Gary and Thompson as the first three defensive linemen (in that order) taken on the opening round. Beathard and Steinberg, who are good friends, normally judge players similarly.

Gary, according to Beathard, is probably the quickest lineman in the draft and has the most talent after Mitchell. He can play either end or tackle, but some scouting services have questioned his ability to play with injuries, since he frequently was out with ailments in college.

Thompson, Beathard said, is a late bloomer "who has all the physical tools, but still needs a lot of polish. He is about the same defending the run and rushing the passer."

Harty is the best available at tackle, a spot where the Redskins are particularly lacking in depth.

Steinberg predicted the Redskins would take a running back, UCLA's Freeman McNeil, the No. 2 rated runner (behind George Rogers) in the draft. McNeil is considered a good receiver and a strong rusher, but he doesn't have breakaway quickness, something the Redskins need in the backfield.

"He'd be tempting if he is available," Beathard said. Beathard also likes Jarvis Redwine from Nebraska, who is quicker than Rogers, and James Brooks from Auburn, who is somewhat small.

There will be many temptations for Beathard, since a number of quality players should be left by the ninth pick. For example, there are at least four outstanding offensive tackles in the draft: USC's Keith Van Horne, Pittsburgh's Mark May, Stanford's Brian Holloway and Washington's Curt Marsh. Van Horne should go early, but at least two of the others should be available come the Redskins' turn.

Following are the players who have the best chance of being selected by the Redskins in the first round of the draft: Defensive Linemen

Keith Gary, Oklahoma, 6-3, 268; Donnell Thompson, North Carolina, 6-4, 265; John Harty, Iowa, 6-4, 255. Offensive Tackles

Mark May, Pittsburgh, 6-5, 278; Brian Holloway, Stanford, 6-6, 265. Running Backs

Freeman McNeil, UCLA, 5-10, 215; Jarvis Redwine, Nebraska, 5-11, 200. Quarterbacks

Rich Campbell, California, 6-4, 220; Neil Lomax, Portland State, 6-3, 212