Despite last week's nightmarish performance against Miami, Redskins Coach Joe Gibbs has resisted the temptation to abandon his training-camp master plan and go all out to win Saturday night's exhibition game against Tampa Bay.

Instead, Gibbs says he will use the game to continue his evaluation of young players and major problem areas. But he admits it's sometimes difficult to follow that course.

"As a coach, you always have to keep in mind what the purpose of these games is," he said about the 7 p.m. game (WJLA-TV-7). "I'm certainly not going to risk playing Joe Theismann in the fourth period just to win. I want to win as badly as anyone, but we need these games to also help us make decisions."

Gibbs must find out if he really has the quality depth he expected entering training camp. Or was last week's poor showing by reserves a better picture of reality?

The closer it gets to the regular season, the more the coaching staff will concentrate on preparing the starters. The performances of many rookies and inexperienced players in this game may be major factors in their quests to make the final roster.

Cornerback Vernon Dean (No. 2 draft choice, 1982), linebacker Larry Kubin (No. 6, 1981) and receiver Charlie Brown (No. 8, 1981) appear to be safely on the team, unless their performances fall off drastically.

Dean most likely will be a nickel back and possibly early-down relief for Joe Lavender. Kubin is making fine progress in the middle and could become a blitzing specialist. Brown was hindered by a midcamp injury but has started to play well again. Other youngsters have less security:

Receiver Carl Powell (No. 3, 1982) is struggling and needs a standout performance against the Buccaneers. The Redskins knew he was a raw talent who would need plenty of work, but he still hasn't developed as quickly as they had hoped and has never shown the speed that attracted them initially. He also has been matched up against some unexpectedly good competition: free agents Rodney Goosby and Chy Davidson, both prospects to be the fifth receiver if Gibbs decides to keep that many.

Defensive end Todd Liebenstein (No. 4, 1982) should get more playing time after a good night against the Dolphins. The Redskins always have projected him for help in the future, when he gains 20 pounds, but he could be used as a pass rusher this year if he continues to improve.

Tight end Mike Williams (No. 5, 1982) also began slowly but may emerge as a solid prospect. He finally is catching on to Gibbs' complex offense and his blocking has improved. He could wind up replacing Rick Walker when the Redskins go with two tight ends. Another tight end, Clint Didier (No. 12, 1981), is bothered by shin splints, but has played as well as Williams nonetheless.

Linebackers Lemont Jeffers (No. 6, 1982) and Jeff Goff (No. 12, 1982) were early summer standouts who have fallen off. Goff will get added playing time this week, but both will have to show exceptional special-team ability to make the roster. Jeffers has to be more aggressive and Goff must get stronger.

Guard Gary Sayre (No. 5, 1981) is having pass protection problems and has fallen behind veterans Melvin Jones and Fred Dean in the race for backup guard. Tackle Don Laster (No. 12, 1982) remains a prime roster contender.

Tampa Bay should provide a good test. The Buccaneers beat Philadelphia last week by scoring 21 fourth-quarter points. But quarterback Doug Williams, who is injured, may not play.

The Redskins have signed veteran defensive end John Lee, who was released this week by Chicago, his third NFL team. Lee, whose strength is rushing the passer, probably will play against Tampa Bay. He has been in the league since he was drafted by San Diego in 1976 . . . Tampa Bay announced that running backs Jerry Eckwood and James Owens and defensive back Johnny Ray Smith will miss the Washington game because of injuries. Center Steve Wilson and linebacker Andy Hawkins are questionable.