Ed Tapscott, a 28-year-old native Washingtonian who became a part-time assistant basketball coach four years ago to help pay his way through law school, yesterday was elevated to head coach at American University. He replaces Gary Williams, who resigned Monday to become coach at Boston College.

Tapscott, a 1971 graduate of Sidwell Friends School and 1975 graduate of Tufts University, had been Williams' No. 1 assistant the past two seasons when the Eagles won 45 games, with consecutive 20-victory seasons and postseason tournament bids for the first time.

The appointment comes as a mild surprise because Bob Frailey, AU's athletic director, had said Monday he was uncertain about Tapscott's coaching experience. Yesterday, Frailey said, "I found out a lot of things I didn't know about him--all of it good. He's a tremendously talented individual."

No other candidates were interviewed formally, Frailey said. Terms of Tapscott's contract were not disclosed. The school has called an 11 a.m. press conference today to introduce Tapscott, who has a large family in Washington, including Marty Tapscott, a cousin who is assistant D.C. police chief.

"It's probably a surprise to a lot of people, including me," Tapscott said, a few minutes after becoming AU's first black head basketball coach. "But it's a very, very pleasant surprise, obviously. With everyone returning, these are Gary's group of athletes. But I was part of Gary's coaching administration.

"I don't think you'll see any major changes in style. Gary and I have different personalities. But, with this group, it would be crazy to do anything differently (on the court) than we've done the past two years. We'll use pressure defense and run the ball up court, trying to play the whole 94 feet."

Tapscott had been strongly endorsed by Williams and the AU players, who met with Frailey Wednesday afternoon. Asked what he remembered most from that meeting, Frailey said a statement by Juan Jones, the team's 6-foot-7 starting center: "We have total confidence in him."

But Tapscott's appointment surprised Jones nonetheless. "Definitely," he said, "because Frailey is one man who's so honest with you. He won't lie. We asked him if Eddie was going to get the job. He said, 'We don't know. We're not sure.' "

But, after that meeting, Frailey became sure. He said he found out that in his only other year of coaching experience, following his senior year at Tufts, where he played point guard, Tapscott coached the freshman team to a 16-3 record there; that Tapscott was in charge of AU's defense, charting it and adjusting it at halftime of games; that Tapscott was impressive as a person to AU administrators, alumni and parents.

"I talked to maybe every facet that covered his life," Frailey said. "I'm confident he's the man."

Tapscott, who graduated from AU's law school, but has not taken his bar exam, agreed that Williams "is a tough act to follow. All you can do is go out, work your hardest and do the best you can. Certainly, I've had an excellent teacher."

With the graduation of no one and the return of Michael Wade, who played as a freshman two seasons ago, Tapscott has only two scholarships to use. He is seeking a point guard, reportedly having a commitment from Mackin's Darnell Swinton, and a big man. Tapscott said he would give Fran Dunphy, AU's other assistant, an opportunity to become his chief aide.

The current players are aware that there is a big difference between being an assistant coach who is friendly with the players and being a head coach responsible for all decisions.

"Togetherness is essential," said Jones. "We're only talking four letters next season: NCAA. You must have confidence and faith in Ed's word. Don't question the guy, because he's the coach. He's going to say some things wrong. He's going to be a little shaky at times, but who isn't, coming from assistant to head coach?

"Mr. Frailey asked us the question, 'Can he keep morale up?' I know he can. If I saw it (not) happening, I'd take the step personally (to correct it). We want to make sure things go right for Ed and the team."