Julius Erving, the good doctor of basketball, admits he made an improper diagnosis last fall. He thought the Washington Bullets were suffering from a serious illness: championship blahs.

"I didn't think they were as good as they looked winning the title last year," said Erving. "I felt they'd have a letdown and wouldn't beat my team (the Philadelphia 76ers) for the division title.

"But the championship obviously has done more for them than I figured. They have exceeded the expectations of a lot of critics, including myself."

Even Coach Dick Motta wasn't sure how well his veteran-dominated club would do over the course of 82 games, when motivation is as important as talent.

But Washington has ridden the momentum fron last year's unexpected championship to the verge of the league's best record this season. In the process, the club has emerged as the odds-on favorite to win another title, although no NBA team has won back-to-back titles in nine years.

"I like their chances of repeating, I really do," said New York Coach Red Holzman. "They have a hell of a good club. They have a lot of strengths. They are the ones everyone is going to have to knock off."

Even if they don't win that title, the Bullets already have achieved a major breakthrough. They have won the respect of their peers, something their heroics last June did not seem to accomplish.

"It's a shame," said Cleveland Coach Bill Fitch, "but it took some time for their reputation to catch up with their championship. Maybe no one believed what they did last year was for real, but they do now.

"This is a legitimately good team. You've got to respect them."

In the eyes of some critics, the Bullets' scenario this season was hardly the stuff of great expectations. Many people thought they might get off to a fast start, thanks to the confidence gained from the title. But once that wore off, the assumption was, they would fall back into the pack and lose the division crown to Philadelphia, although qualifying for a playoff berth.

"I know people weren't sure if we had sustaining power because of our poor record of last year," Motta said. "I was certain we had a great playoff team; that's the way we want it. But things are different in a seven-game series than they are ovre 82 games. You never know how players are going to react." Playing Hard

The Bullets reacted by playing hard almost every night out. They were stunned in the early weeks by an obvious lack of respect for their championship and, from then on, were dedicated, as guard Tom Henderson put it, "to prove all of our doubters wrong."

Said Erving: "Last year, they put it together in the playoffs but they didn't have that exceptional of a regular-season record. They surprised everyone but themselves by winning the title."This year they have won a heck of a lot close games on character and intensity alone and they have beaten a lot of teams they were supposed to beat. That's a sign of a very good basketball team."

Interviews with players and coaches throughtout the league pinpoint three reasons for the Bullets' success this season: their front court, their bench and the carry-over effect of last year's championship. Strength Up Front

"People talk about their fron line being the oldest in the league and all that," said Milwaukee forward Marques Johnson, "but the way they play together is something. They know each other's strengths and they use them.

"They've also been there already; they know what it is like now to win. That experience is invaluable. They believe that when they want to win, they can. It's a nice feeling to have."

New York center Marvin Webster, who played for Seattle against the Bullets in last year's final round of the playoffs, has noticed increased confidence this season among the Washington players.

"If you are a team like the Bullets," he said, "and you make the playoffs so many times and you don't win, you get to a point when you start worrying about your real ability because you keep losing.

"By winning, you immediately gain a lot of confidence. Look what they did last year: they came a long way from the regular season, they won the championship and they did it away from home.

"It's going to be very hard for anyone to beat them. The only thing I can see is that they have worked so hard in the regular season it might catch up to them in the playoffs."

New Jersey Coach Kevin Loughery is convinced that as long as their bench holds up in the playoffs, fatigue from the regular season won't bother the Bullets.

"They've got a super team," said Loughery. "They've got that great bench wich keeps everyone fresh and they have outside shooters and all that depth inside.

"They can play defense when they have to and they can sag so well they make you beat them from the outside, and that isn't easy to do. They are the best team in the league right now."

The Bullets' depth can create frustration for opponents, who start thinking they have mastered Washington's starters just when the subs start coming in.

"It gets to you," said Cleveland guard Austin Carr. "They can put out a second team that is just as strong as the first. It wears you down. You wonder when the talent is going to stop coming out onto the court.

"Having a bench like that keeps people fresh and gets opponents off guard. That's what separates them from everyone else right now."

Holzman likes the Bullets mixture of "good young reserves with a lot of experienced players. It's a good balance. The extra year has helped all of them. They are better players now than they were last year."

As Johnson put it: "Sometimes the guy they bring off the bench is better than the guy he replaced. And the matchups can be something else. Like sometimes I have to guard Mitch Kupchak and that is pretty hard for a small forward. Too Much Depth

"They've also got four guards who can play. They have confidence in their offense and in their abilities."

Cleveland's Fitch, however, remains more than depth, is the reason for the Bullets' success.

"They know where they have to go to win," he said. "They will get the ball down low on you and ram it down your throat every time they can.

"You've got to admire them for staying with what is working well for them."

Despite Washington's power, this is not a frightening team. Opponents respect the Bullets and priase them, but they don't run from them. The Bullets have weaknesses, and no one is conceding them a second championship.

"I think they are the cream of the league right now," said Philadelphia Coach Billy Cunningham. "But we have won three of four from them this year so we know they can be beaten.

"In the playoffs, you have to get the breaks, you have to have everyone healthy and playing and everyone has to be mentally and intellectually sharp. You break down in any of those areas and you can lose.

"My team is starting to play well, for example. I think we will be a factor in the playoffs. But to to anywhere, we are going to have to get past the Bullets." No. 1 Target

This will be a different playoff atmosphere for Washington. Last year, after a horrible finish, the Bullets limped into postseason paly not expecting to accomplish much. They never had the home-court advantage after the miniseries with Atlanta, nor were they ever clear-cut favorites to win any round.

This year, they will be the No. 1 targets from the first time they step onto the court. They will have the benefit of the home-court edge, but they also will have to deal with the pressures of being the fox trying to keep ahead of a baying pack of hounds.

"It doesn't really matter how well you play in the regular season or by how many games you win the division," said Erving. "It starts all over again in the playoffs. We have found that out the last couple of years."

If the Bullets encounter a major injury during the playoffs, if Motta can't find at least one hot-shooting guard every series, as he could last year; if one of his veteran front-court players slumps, Washington will have to scramble to defend its title. But Denver Coach Don Welsh thinks anyone who believes "this is a one-dimensional club" is badly mistaken.

"They can run, they can play the transition game, they can play defense, they can shoot from the outside, they can hurt you inside," said Welsh. "This is a versatile, confident team. They've worked hard to get where they are."

And now that they have made it through the perilous waters of the regular season, overcoming injuries, never losing more than two games in a row after Octoberl and receiving quality performances from at least nine players, Motta thinks the real Bullets can stand up.

More than anyone else, he realizes that the true strenght of his team is its ability to handle the pressure of the intense playoff series. This is a team of self-motivators who have no problem inspiring themselves to play in these games. And this is a team that prides itself on having the flexibility to adjust to the intricacies of playoff basketball.

"There is nothing quite like the playoffs," said Motta. "You can really scout an opponent and learn their strengths and weakness and study films anf work on matchups.

"Strategy is important. And there is more stability and you don't have to worry about the rigors of travel as much. We've got the experience and the depth and the talent you need to do well in the playoffs." New Experience

But this will be a new experience for bot Motta and his players. They never before have been the defending champions.

"We've lived with that title throughout the regular season," he said, "and we've done better than a lot of people thought we could.

"I've said it right along. We are our own worst enemies. We can win it again and we know it. We just can't go out and beat ourselves . If we do, we'll have no one else but ourselves to blame because we know, when we are playing right, there is no one in this league who can handle us." CAPTION: Pictures 1 through 3, Reserves help make Bullets a formidable playoff team: from left, Charles Johnson, Larry Wright, Greg Ballard in action. Photos by Richard Darcey-The Washington Post