Cornerback A.J. Johnson, who underwent reconstructive knee surgery in the offseason and wasn't expected to play this year, informed Coach Joe Gibbs yesterday that he's ready to play.

Gibbs said defensive coaches will evaluate Johnson in practice this week, but wouldn't rule out his being in uniform for Sunday's game against the Miami Dolphins at RFK Stadium.

If he is, it would mark one of the most amazing medical stories the Redskins have had. He underwent the surgery in June, and doctors generally say that at least six months of rehabilitation is needed. Johnson was almost ready to practice in about four and was back on the field doing all work in five.

He has been practicing for about a month, and coaches have been waiting for him to feel totally secure about the knee.

Johnson, 23, could make a difference as the season concludes. Cornerbacks are one of the most valued commodities in pro football and the Redskins think he has a chance to be a good one.

"He has a fire about him," Gibbs said. "He was a real plus for us, a valuable guy. We'll wait and see before making a decision. It depends on how all of us feel. He has looked good and we wanted to wait until he was champing at the bit to get back out there."

Johnson said that's exactly how he felt, saying: "I think I'm ready. I'm able to go out and play, and I'm not thinking about the knee. I know they told me I wasn't going to play this year, but I was hardheaded about it. I wasn't going to let that sway me."

He started as a nickel back last season as a rookie and won a full-time job when Darrell Green got hurt and Brian Davis was benched. He led the Redskins with four interceptions and eight pass deflections and was 10th in tackles with 55. He also was seventh in the NFC in kickoff returns (21.0 yards).

He made one of the Redskins' big plays of last season when he had two interceptions, including one he returned for a touchdown, in Week 13 against Phoenix. He was named NFC defensive player of the week. Coleman Likely Out

The news on linebacker Monte Coleman isn't so good. He pulled his right hamstring while chasing Dallas tight end Jay Novacek on Thursday and probably won't play this week. "It was bothering him even before he came out of the game," trainer Bubba Tyer said. "We'll take it day by day. He's pretty sore right now."

Tyer said guard Mark Schlereth was moving better on his sprained right ankle; he might play. Ricky Sanders (ankle) and Greg Manusky (thigh) are expected to play. . . .

The Redskins have fallen behind in five straight games and haven't scored first since Oct. 14 against the Eagles at RFK. . . . The Dolphins will be the eighth straight team playing the Redskins after a victory. The last team that lost the week before playing Washington was the Phoenix Cardinals in Week 3. . . . Gary Clark moved past Bobby Mitchell and into fourth place on the Redskins' career reception list last week. He had eight catches for 74 yards and has 399 for his career. Mitchell has 393. Clark needs 22 catches to tie Jerry Smith for third place. . . . Earnest Byner's 604 yards are the second-highest total of his career. He had 1,002 in Cleveland in 1985.