Mark May, the Redskins' 1981 No. 1 draft choice, has lost his starting left tackle position for Sunday's game against St. Louis in RFK Stadium. He will be replaced by Joe Jacoby, the rookie free agent who has missed the last two weeks with a twisted neck.

The decision to replace May, who has started at left tackle since the first preseason game, was made by Offensive Coordinator Joe Bugel, following May's subpar performance against New England last Sunday.

"I just felt Mark was slipping in his techniques," Bugel said. "He is making the same technique errors he made at camp.

"We're not giving up on Mark. He's a player, no question about that, and he was doing a good job. But maybe it will be good to give him a break, let him catch his breath and sit in the bullpen for a while. He's taken a battering and I think it's worn him down a little."

Bugel said Jacoby, who has started this season at left guard and right tackle, deserved a chance, "because he's played well every time we've used him, and that's what you have to base these jobs on."

Neither Bugel nor Coach Joe Gibbs would say whether May's demotion also was the end of the team's attempt to convert the rookie into a left tackle.

May had been a right tackle at Pittsburgh, where he won the Outland Trophy as the nation's top lineman last year. When he first joined the Redskins, he had problems with the left side, but adjusted well early in camp as a replacement for the retired Terry Hermeling.

Now Bugel says May will be tried again on the right side, as a backup to veteran George Starke.

"Mark will be our swing man, he'll play both sides," Bugel said. "Is that the end for him on the left? That's a tough question right now. I will decide that after I see him again on the right. If he is significantly better on the right, that will help our evaluation."

May said he could sense "something was going on" during Monday's film evaluation meeting, but he didn't know he had lost his starting job until practice Wednesday.

"You can get ticked off about it, but what good does that do?" he asked. "I can't let it bother me. I'm trying to relax. Maybe this will help. I had been feeling a lot of pressure and that certainly is gone now. I've never been in this position before, where I had to watch someone else play, so it's going to be a strange experience Sunday."

May admitted he was having problems, especially on Sunday, when he was trying to block New England's Julius Adams.

"I was worried about him instead of worrying about my techniques," May said. "Joe (Bugel) is just a real technican coach. It's been tough for me to pick it up, the way he wants it done. It's a lot different from college.

"I've been having particular problems with my left hand. I haven't been able to use it to lift people up and drive them back. It's hurt me on my run blocking. The first few games, I had problems crossing my legs on pass blocking, but I got that straightened out. Now it's this."

May, who has been playing despite a broken nose and hip pointer, was victimized early in the season by defensive ends who beat him to the outside en route to sacking quarterback Joe Theismann. But that problem was alleviated when the team went to two tight ends, which gave May outside help.

"I thought I was playing well," he said. "But maybe I've let the pressure get to me. This is different, it's not like a regular job. You have to be certain places at certain times or it costs you money. You may think you are playing well in a game, but you see the films on Monday and find out you are messing up. It's hard to explain, but I could feel it build up.

"I think I can handle what's happened. I watched Riggo (John Riggins) when Wilbur Jackson replaced him as a starter. John just kept working and didn't complain. He went about it like a professional and that's what I'm going to do."

Gibbs said both Jacoby and May "are part of this team's future. They both are going to play a lot. All this is just part of a continuing shuffling process that we've been undergoing.

"May showed he was a fighter. He stayed in there despite the broken nose and the sore hip. I think we owe it to him to try him on the right side and see how he does. He's exhibited some good things on the left and now it's time to see him on the right."

Jacoby was one of the major training camp surprises, making the team as a reserve tackle. But he got his first start as a guard six weeks ago in place of Russ Grimm, who was out with a sore knee. Jacoby then took over at tackle for Starke, who broke his right hand, and remained a regular until hurting his neck against Chicago Oct. 11.

When the Redskins drafted May, the team's master plan for the future had May and Jerry Scanlan emerging as the eventual starting tackles. Jacoby later would be signed as a free agent from Louisville, thanks to the salesmanship of scout Charlie Casserly, who convinced the Washington front office that Jacoby was a potential pro.

Now Jacoby is a starter, May is on the bench and Scanlan's future is in doubt. He underwent surgery yesterday at Sibley Hospital to remove a herniated disk in his neck. It is an operation that has prevented some players from returning to football.

Tight end Rich Caster had both cartilage and ligament damage repaired yesterday, also at Sibley. He will be in a cast for six weeks, according to Gibbs, and is lost for the season