Running back Gerald Riggs returned to practice for the first time since spraining his left arch last month, and ran freely and without pain and said he should be ready to play by the end of the regular season -- Dec. 30 against Buffalo at RFK Stadium.

The absence of rookie running back Brian Mitchell for a second straight day gave Riggs more carries than he normally would have gotten, and they came on the hard artificial turf practice field at Redskin Park.

"I don't think I've lost much," Riggs said. "I've worked pretty hard and been anxious to get back on the field."

Riggs doesn't know when he'll be activated, although before the game with Buffalo is a good guess. Gibbs has said he's hesitant to make roster moves while the Redskins are winning, "but if we thought it'd help our team, we wouldn't hesitate."

Riggs, getting accustomed to a new orthotic that team officials hope will prevent a recurrence of the injury, said he'll be patient.

"Right now, we're playing it by ear," he said. "I'm not going to come in and mix up anything, and Coach Gibbs has too much on his mind besides me right now. I could probably be ready to go next week. I need to move around on it as much as I can and see what I can withstand."

Gibbs said he was pleasantly surprised by Riggs. "Gerald looked good for the first time out," he said. "He's as healthy as he's going to be, and I thought he looked good. I expected him to look sluggish the first time out." Running Backs Report

Mitchell is due back at practice today after spending two days in Louisiana with his father, who suffered a serious heart attack. "He's very sick, but they feel they've got him stabilized," Gibbs said. . . . Gibbs has said one of his priorities down the stretch is keeping Earnest Byner fresh. Byner has averaged 28 carries a game since Riggs got hurt and his 255 carries and 1,031 yards are already career highs.

"I'll just continue to work and work hard when I'm in there," Byner said. "There are certain circumstances I won't do as much as I was doing early in the year. Really, I'm not going to change anything. Usually at this time of the year is when things start turning over. Hopefully, I got another year left and I won't start wearing down." Koch Doubtful

Defensive end Markus Koch (knee) didn't practice yesterday and is doubtful for Saturday night's game at Indianapolis.