One question that 22 opposing general managers have been asking themselves as the Boston Celtics began the defense of their NBA championship: Can a team that won 61 and 62 games the past two season still be improving?

Considering all the things that can happen -- injuries, questionable calls by officials at critical times, travel problems, fatigue, dissension -- when a team loses only 20 times while traveling America from October to April it is, indeed, a remarkable achievement.

Dismissing for a moment the presence of Larry Bird, whose all-around ability generates success, the single most important ingredient the Boston Celtics own is depth.

In tonight's matchup between the haves and the have-nots at Capital Centre (8:05, WTOP-1500), one of the most obvious differences between the Celtics and the Bullets will be the quality of the reserves.

At the begining of the second quarter, Coach Bill Fitch will insert fresh young legs belonging to Kevin McHale, Rick Robey and Gerald Henderson. That trio, often with help from rookie Charles Bradley, not only holds its own, it usually increases the lead the regulars have built.

In the Bullets' opening 124-100 loss at Boston, the subs accounted for a 31-18 advantage in the second quarter after the starters could gain only a six-point lead. In the Celtics' 129-89 blowout of Detroit Saturday night, the reserves took a 35-27 lead and expanded it to 63-42 by halftime.

"I expect to have the advantage in the second quarter," Fitch said. "Our subs have played together for three years now. They know each other and have as much confidence as the starters."

Although the Celtics don't have the high-scoring sixth man of their chief rivals, such as Milwaukee's Junior Bridgeman and Philadelphia's Bobby Jones (now a sometime starter), they have someone who is becoming just as valuable.

The rapid improvement of McHale, a second-year forward from Minnesota, is the main reason why the Celtics could be even better this season.

In five games, the enthusiastic, personable native of Hibbing, Minn., is averaging 13.6 points, 7.8 rebounds and 2.8 blocked shots while playing 23 minutes a game. There are many starting forwards who would give up their Nike contacts for those statistics.

"Kevin worked very hard in training camp," said Fitch. "He's playing with a lot more confidence this year and, of course, he learned a lot last season."

McHale almost passed up his chance to hook on with the eventual champions. After being the third player selected in the draft, negotiations with the Celtics broke off and he went to Italy to sign with Trieste.

"Let him eat spaghetti," was Fitch's parting shot, but literally hours before the signing was to take place, the Celtics relented and McHale returned.

After a slow start, the 6-foot-10, 230-pounder steadily earned more playing time with his aggressive rebounding and shot-blocking. He started just one game, when Cedric Maxwell was injured Dec. 2, scored 21 points and grabbed nine rebounds. He blocked six shots against Milwaukee and was in and out of the league's top 10 in that category all season, finishing with 151 to go with his 10-point scoring mark.