In mid-September, Dave D'Addio's name still was on Maryland's football roster, but its appearance there seemed almost an afterthought. He had missed the entire 1981 season because of an injured right knee and the first two games of this season with a pulled groin.

So it was to be expected that when No. 44 lined up in the backfield the third week of the season, against North Carolina State, most of the people in Byrd Stadium didn't know who the player was.

Five games later, D'Addio is no longer an afterthought at Maryland. He's the healthy redhead, the one who runs like John Riggins, the one who gets as much pleasure running over defenders as he does by running around them.

"I'm pretty excited about staying healthy this year," D'Addio (pronounced Daddy-oh) said yesterday. "After the knee injury, about the third day of spring practice two years ago, I was sort of down, pretty upset. I tried to rush the recovery and it hurt me in the long run. Dr. (Stan) Lavine told me he just wanted me to walk.

"Then, this year, it really hurt me not to be in the first two games. I was so excited about going to Penn State. By the time I got to play, my running was not what it should be. But I'm starting to feel good again."

When D'Addio feels well, defenders feel pain.

"Let's just say that Dave is a big, strong, aggressive guy who will run over you," said Tyrone Furman, a Maryland defensive guard. "He doesn't care, he'll punish a defensive player whenever possible. He deals out a lot of punishment."

D'Addio's brutish, straight-ahead style of running, plus the No. 44 on his uniform, has caused many Terrapin players to call him "John Riggins" or "J.R." At 6-foot-2, 230 pounds, D'Addio bears a remarkable resemblance to Riggins' physique.

It's not an accident.

"The Riggins thing is mostly a joke," D'Addio said. "But he's definitely my idol. I grew up watching and admiring him and his running style, the way he can run through people. I don't have the moves to juke people, so my style is similar, I guess."

D'Addio's best rushing performance of the year came last week against North Carolina, when he gained 61 yards in nine carries, including an 18-yard touchdown sweep that demonstrated his 4.7 (40-yard dash) speed.

"He's done an outstanding job," said Jim Cavanaugh, Maryland's running back coach. "He's regaining his speed and flexibility, and his blocking has been superb. He knows how to run north-south, which is what you want your fullback to do."

D'Addio, from Union, N.J., came to Maryland primarily as a running back. But because of injuries on defense, former coach Jerry Claiborne switched D'Addio to linebacker, a position he played the full 1980 season.

"Defense was fun when all I had to do was fly to the ball," D'Addio said. "But it wasn't as much fun when I had to actually learn the defensive schemes and how to protect myself."

D'Addio was recruited by Nebraska, Georgia and Tennessee, among others. Many colleges wanted him to play defensive tackle or tight end.

"But when I visited Maryland," D'Addio said, "guys were genuine. It was more than just 'Hi, how you doin'?' Dave Pacella (an offensive tackle) showed me around and I really liked the place."

"D'Addio was one of about 12 guys that were visiting that weekend," Pacella said. "I piled all of them in my car and we were driving back to the dorm at about 4 a.m., when a policeman pulled us over and gave me a ticket for having too many guys in the car. Each of them gave me about two or three dollars to pay the ticket, but I never had to pay and kept the money.

"It was a great weekend, but that's what convinced him? I'm just glad he's here."