CARLISLE, PA., JULY 3 -- Almost from the moment Mark May was helped off the field at RFK Stadium last fall, the Washington Redskins knew he faced a grueling rehabilitation that would have some good days and some bad ones.

Today was one of the bad ones. As the Redskins welcomed their full squad -- with the exception of four holdouts -- to the opening of two-a-day practice, they also got some depressing, but not unexpected, news about one of their favorite Hogs.

Eight months after undergoing reconstructive surgery on his right knee, May will be back in the operating room Thursday for doctors to perform an arthroscopic procedure "to shave down some rough edges in the knee," Redskins trainer Bubba Tyer said.

Tyer estimated May's eventual return would be delayed perhaps as few as 10 days because of the procedure. But May began this camp in shorts and the Redskins held out a small amount of hope he could return for the start of the regular season.

Now, Tyer's best guess is that May could return in October after missing four or five regular season games.

"It depends," Tyer said. "It's really a minor procedure, but he may have some bleeding and swelling. You just have to see how he reacts."

Tyer said doctors had been considering the operation for a while, but had put it off to see how much progress May made the first week of camp.

May and fellow Hog Joe Jacoby have spent this camp in shorts, and today donned shoulder pads (and shorts) briefly to watch their teammates. Mostly, their work is done inside the locker room, where both are spending torturous hours on Cybex resistance machines and doing other leg exercises.

Jacoby may be allowed limited contact work as early as next week.

May declined to comment, but it's likely today's news was upsetting for someone who has been fanatical about his rehabilitation since undergoing surgery Nov. 7.

His absence means one less roster move in an area that Coach Joe Gibbs calls "probably our toughest decisions." After Jacoby, May and Russ Grimm were injured last season, the Redskins turned to several young players and Mark Schlereth, Ray Brown, Ed Simmons and Raleigh McKenzie performed well. Now, with Grimm beginning camp as the starting right guard, Jacoby perhaps coming back next week and the addition of Plan B signee Mark Addickes and third-round draft choice Mohammed Elewonibi, coaches face some hard choices in deciding on youth or experience.

"I know it's tough for Joe and Mark," Grimm said. "It wears on you more mentally than anything else. You're itching to get back out there and you've got to wait for doctors to tell you it's okay. Practice is not fun, but you want to be part of it, come in and sit down and drink a cold one and talk about it. When you're not out there you miss it."

Meanwhile, as expected, defensive linemen Darryl Grant and Markus Koch, linebacker Ravin Caldwell and running back Gerald Riggs -- all of them unsigned -- missed the first day of workouts.

No resolution appears on the horizon, although General Manager Charley Casserly talked with agents and players today. But Casserly emphasized that, while he was willing to talk, negotiations are over.

"We made what we think are fair offers," he said. "We tried to get them here. We don't try to squeeze guys. We have the second-highest payroll in the league."

One of the players Casserly spoke with was Riggs, and it appears a solution may be near. Sources say the two sides have agreed on what the four-year package should be worth in total dollars but disagree on how the money will be paid out.

Riggs and his agents want the contract front-loaded. They want, for instance, a $100,000 roster bonus and other similar payments upfront. The Redskins want bonuses paid after the season and based only on performance. That would protect them in case Riggs has some of the same injury problems that sidelined him about half of last season.

Casserly apparently has made it clear that what's on the table is all that's going to be, and Riggs is thinking about what he should do.

Likewise, it appears the gap between Caldwell and the Redskins has narrowed considerably.

Koch and Grant are another matter. Sources indicate that Grant and the Redskins are about $200,000-a-year apart on a three-year deal, while Koch and the Redskins are about $100,000-a-year apart on a three-year deal.

One veteran who did quickly end his holdout was safety Todd Bowles, who arrived around midnight and signed his contract this morning.

Bowles, who made $250,000 last season, signed a two-year contract with an option for 1992. He'll receive a base salary of $350,000 in 1990 and about $1.2 million over the three years.

He decided to take the offer that had been on the table for several days after a Sunday phone chat with Casserly. He then drove to Baltimore to discuss the matter with his agent, Tony Agnone, and arrived at camp a few minutes before midnight.

"It was important to be here," Bowles said. "You know the playbook and all that, but you've still got to come in here and get your body in shape. I got what I felt was fair, and I signed. My agent didn't disagree."

The last few days had been "pretty stressful," he said. "You think it's going to work out, but you never know."

Until Riggs arrives, the spotlight will fall on Earnest Byner and veteran James Wilder, a Plan B signee. Since Byner ended last season as the starter, he begins this camp that way, but his competition with Riggs was expected to be among the most spirited of camp.

A year ago, Byner was shifted to H-back, but the emergence of Jimmie Johnson may keep him in the backfield. Regardless, Byner arrived with a smile and the standard "I'm-ready-to-roll" speech.

"I'm not thinking about competition with Gerald or anyone else," he said. "I just came here to have fun and make a living for my family. It probably will end up being real competitive, but that's part of the game. Gerald has to get what he thinks is fair {in his negotiations}. I'll tell you, I don't envy him trying to squeeze {all the} money you can."

Still, he admitted hoping to stay at running back "because I can help the team more there. And to tell you the truth, the running back touches the ball more and I've got an ego like anyone else's. I want it in my hands."