The ideal linebacker in Gregg Williams's defense needs speed to fit in with the aggressive style of play demanded by the Redskins' assistant head coach. He needs to have sound football fundamentals and be savvy on the field. He needs to be able to play all three linebacker positions. And he is expected to contribute on special teams.

Under Williams's guidance, Antonio Pierce -- up to now an obscure reserve who signed as a rookie free agent in 2001 -- is suddenly in the spotlight as the first linebacker off the bench and a possible opening day starter.

The 6-foot-1, 240-pound defender, who has been predominantly an outside linebacker before this year, has emerged as a critical player for the Redskins. He has learned to play middle linebacker and started in preseason games for Mike Barrow, who has yet to play because of knee tendinitis. Pierce's performance is drawing praise from his coach.

"I think this speaks volumes for Antonio's versatility that he can fit in all of them," Williams said. "He's a linebacker. Linebackers need to be the heart and soul of your special teams and your defense anyway. He's the ideal guy because he can run and hit and play all three."

Pierce, 25, hasn't played a significant role in the NFL since his rookie season, when he started eight games because of injuries to outside linebackers LaVar Arrington and Shawn Barber. Pierce finished with 64 tackles, 48 of them solo, a forced fumble and a fumble recovery, as well as an interception in the regular season finale that led to a victory over the Arizona Cardinals.

Because of Barrow's injury, Williams asked Pierce to start at middle linebacker on Aug. 14 against the Carolina Panthers. Pierce was jittery before Washington's second exhibition, but performed as if he had been playing middle linebacker for years.

"We can't ask the guy to do much more," said linebackers coach Dale Lindsey. "He's done everything we've asked him to do. He's a great competitor, very intense. We count him as a starter. We think we have four starters at linebacker."

The other three are Barrow, Arrington, who plays weakside linebacker, and strongside linebacker Marcus Washington.

The biggest challenge in learning middle linebacker, Pierce said, has been grasping the complexities that separate it from the outside positions.

"It's a big difference," Pierce said yesterday. "Playing outside linebacker you've got a different view on how you see things as far as the play developing. In the middle, you're more in charge of everything. You're a quarterback of the defense. So it's a big difference. Gregg Williams gave me that responsibility. I'm trying to do the most with it."

Washington's annual hiring of a new defensive coordinator -- the team has had four the past four seasons -- helped Pierce adjust to a new system and position. "Being through three or four coordinators," Pierce said, "I've been through enough to adapt to anything."

Williams considers Pierce his fourth-best linebacker, largely because of athleticism. But Williams also likes Pierce because of his cerebral approach to the game and study habits.

"From a coordinator's perspective, I like that fact that's he's an intelligent coach on the field," Williams said. "I'm beginning to trust him like a coach on the field."

After joining the Redskins in 2001, Pierce never envisioned playing middle linebacker. Pierce, who weighed 235 pounds as a rookie, took a look at the bulkiness of middle linebackers such as Kevin Mitchell, who weighed 260, and thought the position was not for him.

In 2002, when Marvin Lewis was the Redskins' defensive coordinator, Pierce was sparingly plugged in as middle linebacker in Lewis's penny defense, which was used to counter three-receiver sets. The formation included four cornerbacks and three linebackers, with Pierce sandwiched between Arrington and Jessie Armstead. Pierce was substituting for Jeremiah Trotter, who was out with a knee injury.

Now, Pierce's role will increase tremendously from last season, when he contributed mostly on special teams. Last year, Pierce finished third on the special teams with 18 tackles, yet limited opportunities left him with only nine tackles as a linebacker.

"His situation in the past I don't know," Williams said yesterday. "But [I like] the fact that he's able to do a lot of things for us, as many packages as we want to play."

Arrington said: "He's a utility guy, all purpose. Whatever you need, he's there for you. He's a special guy. He's a diamond in the rough."

Barrow, 34, started every game last season with the New York Giants, amassing a career-high 150 tackles. However, Barrow's injury makes it uncertain if he will be ready for the regular season opener against the Tampa Bay Buccaneers on Sept. 12.

Even if Pierce doesn't start, Williams said, the linebacker will be used frequently and will be considered a starter. Williams substitutes freely to keep the defense fresh, and is known for using up to 16 defensive packages, including formations using four and occasionally five linebackers.

"You can throw him out there in any situation and he knows what to do," Williams said of Pierce. "From a coach's perspective, there's a comfort [level] there. He's a pro. He's not one of those guys who's looking for attention to come up and chitchat with you. He is preparing every single second of the day. . . . He's been impressive."

The Redskins' Antonio Pierce (58) backs up teammates whenever necessary, stepping in for Mike Barrow at middle linebacker this preseason."Whatever you need, he's there for you," LaVar Arrington says of Antonio Pierce, in hot pursuit of Kerry Collins.