Rookie running back Brian Mitchell was in uniform as expected but didn't play in Saturday's 35-28 loss to the Colts. Mitchell sprained an ankle in the prior week's victory over New England, then re-injured it in practice.

With Gerald Riggs still on injured reserve, Reggie Dupard became Earnest Byner's backup, and he looked very good in gaining 54 yards on 10 carries.

Mitchell is expected to be available for Sunday's game against Buffalo at RFK Stadium, and Riggs also is available if Coach Joe Gibbs decides to activate him.

Byner, meanwhile, continued to roll, gaining 154 yards on 31 carries. He has put together four straight 100-yard games and five in six weeks. The last Redskin to have four in a row was John Riggins in the playoffs after the 1982 season.

Since Riggs got hurt, Byner has averaged 28 carries and 123 yards a game -- an average of 4.4 yards per carry.

He has now rushed for 1,185 yards and has the fifth-best season in Redskins history. He needs 163 yards next week to break the team-record of 1,347 by Riggins in 1983.

His five 100-yard games are the third-most in one season in Redskins' history. Larry Brown had six in 1970 and 1972, Riggs had five in 1984 and George Rogers five in 1986. Candid Camera

The Redskins will report this afternoon for a film session and light workout, then have Christmas off before beginning full practices for Buffalo on Wednesday. . . . The Redskins may start getting anxious about being on ABC-TV. They haven't won an ABC prime-time regular season game since beating Dallas, 13-7, in 1987. Since then, they've lost seven in a row, including games to Philadelphia and Indianapolis this season. . . . Byner is the 11th player in NFL history to rush for 1,000 yards with two teams. He did it in 1985 for Cleveland. . . . Gary Clark is eight pass receptions shy of Jerry Smith for fourth place on the Redskins' all-time list. Smith has 421, Clark 413. . . . The 53-yard Mark Rypien-to-Clark touchdown pass was the Redskins' longest of the season.