Charles Davis has had to grow up very quickly this fall. While almost all except the extremely talented rookies in the NBA are being brought along slowly, the Bullets' first-year forward made his home debut Tuesday night in a starting role against Julius Erving.

That's like playing your first tennis match against John McEnroe or facing Goose Gossage in your first major league at bat. There's nowhere to go but down.

Davis will get a break in Milwaukee Thursday night (WDCA-TV-20) when the Bullets try for their first victory of the season because the Bucks' all-star forward, Marques Johnson, is involved in a salary dispute and will not be in uniform.

The Bucks are so rich in reserves, however, that Coach Don Nelson is able to call on Sidney Moncrief to fill the void. Moncrief, a clone of Denver's David Thompson, took over at guard last season when Brian Winters was injured and averaged 14 points a game. An excellent leaper with great quickness, the 6-foot-4 former Arkansas all-America scored 29 points Saturday in Milwaukee's 119-103 victory over Boston.

"The only way to learn is to go out and play against these guys," said Davis, one of five rookies (and the only second-round pick) in the NBA to earn a starting job. The others: Mark Aguirre, Isiah Thomas, Buck Williams and Kelly Tripucka.

"I wasn't really nervous against Doc," he said of his seven-point, five-rebound effort against Erving in the Bullets' 112-99 loss to Philadelphia at Capital Centre. "I'm going to be playing against a lot of guys who used to be my idols and sooner or later it was going to be him."

The 6-7 Davis is starting ahead of Don Collins because of his ability to rebound, which is an area of great concern to Coach Gene Shue. With 6-7 Greg Ballard playing power forward, Shue strongly believes he needs as many rebounders in the lineup as possible.

At Vanderbilt, Davis led his team in scoring (18.6) and rebounding as a junior, but split his time between guard and forward his final season and his rebounding average dropped from 8.6 to 5.8.

"I'm excited about starting and I hope I can hold onto the spot," he said. "I know what I have to do. All coach talks about is defense and rebounding.

"No. 1 is defense and that's where I've had to work the hardest," the 23-year-old native of Nashville said. "The way Shue wants it played is different from what I did in college. Some habits are hard to break, but I'm working hard and beginning to adjust.

"I'm settling down a lot more lately. In some of the exhibition games, I was getting too excited. I'm tying to learn to relax and not force things. I haven't got all the plays down yet, but they're coming easier."

Shue says he is plesed with Davis' progress and probably will keep him in the starting rotation unless the front-line combination of Ballard-Davis and Rick Mahorn doesn't produce enough points.

"Davis still is in the learning stage," the coach said. "He tries to execute the plays and works hard on defense. He gets out on the break pretty well and looks like a pretty good rebounder."

Frank Johnson, the Bullets' No. l draft choice, hopes to play against the Bucks. The 6-2 guard banged his right ankle on the basket support after driving for a shot against Philadelphia and had to leave the game. However, there was no sprain and very little swelling . . . Former Bullet Bobby Dandridge is expected to make his debut after signing with Milwuakee this week . . . The Bucks were 34-7 at home last season and beat the Bullets four out of five games.