On the eve of perhaps their most important game of the young season against Larry Bird and the resurgent Boston Celtics, the Washington Bullets yesterday put guard Kevin Grevey on the injured list and activated rookie forward Steve Malovic.

Grevey has two injured hamstring muscles. After he saw three doctors yesterday, the decision was made to put him on the injured list. He must miss at least the next five games.

Malovic, a 6-foot-10 rookie from San Diego State acquired from Phoenix for the Bullets' No. 1 draft choice, has missed all the games so far with a sprained ankle.

Grevey, who has had a career-long history of hamstring problems, missed two games last week because of his ailing right leg, then hurt the left leg Wednesday night against the Cleveland Cavaliers.

"His hamstring problems are just recurring too often, now," said the Bullets' general manager Bob Ferry.

"The doctors think he needs about 10 days of therapy and then he has to come back slowly. He's still taking some extensive tests to see if there is anything physiologically wrong."

The Bullets' other injured guard, Roger Phegley, who has a sprained ankle, is listed as quiestionable for tonight's game. But Coach Dick Motta said the injury is not serious and it is possible Phegley could play.

Phil Chenier, who has started the last three games in Grevey's place, will start again tonight and, if Phegley can not play, Gus Bailey and Larry Wright will fill in as the backup shooting guard.

A sellout crowd of 19,035 is expected at Capital Centre for the 8:05 p.m. game and most will be there to see Bird. One of the game's best passing big man, Bird is also the Celtics' leading scorer and a primary reason they are off to a lightning start this season. Boston has won seven of nine games, three straight on the road.

At the opposite end of the floor tonight, seated probably at the end of the Bullets' bench, will be Bailey, a free agent playing for little more than the NBA minimum salary of $30,000 a year compared with Bird's $650,000. But in his own, less spectacular way, Bailey has become almost as valuable to the Bullets as Bird is to the Celtics.

The fans don't come out to see Bailey and many of them still do not know who he is. But with his present injury situation, Motta does not even want to imagine what it would be like not having Bailey right now.

He is one of those players Motta says he can turn to at any time and in practically any situation and feel comfortable with him in the game.

Motta says flatly that the Bullets would not have beaten Cleveland Wednesday if not for Bailey.

Grevey and Phegley had left the game in the second quarter with injuries and Kevin Porter was not as effective as he had been earlier, so Motta called on Bailey to run the team. He played the final 10 minutes, nearly flawlessly. He scored six points and had seven rebounds and two assists. More important, he did not have a turnover.

Despite that game, and Motta's praise, Bailey still is not looking at tonight's game as his "big chance."

"I never take anything for granted in the NBA anymore," he said. "If I play, I'll be gratefu. But if I don't, I'll still be there cheering.

"Coach Motta hasn't sat down and talked to me and told me anything special. You know what's expected of you and coaches don't have to keep telling you."

Bailey signed with the Bullets as a free agent a few days before training camp opened. He came as a defensive specialist and as an insurance policy. The Bullets wanted protection in case Grevey did not sign a new contract, Phil Chenier could not come back from his back injury or Phegley did not work out.

Bailey has been impressive from the first day and his value has increased as the season has progressed.

At 6-5, he is the Bullets' best defensive and rebounding guard and he runs the offense well. He also is capable of playing as the shooting guard.

He has adjusted to being a spot player, knowing that some nights he will have a chance to be a hero, and that other nights he will get off the bench. That has happened twice already this season.

"I still know it's a numbers game," he said, "and as a result, I can't feel secure. I'm just glad I got a chance to play and show what I can do.

"I'm in limbo and I really don't know what will happen," Bailey added. "I haven't an apartment of my own yet because I don't know how long I'll be here.

"But whatever does happen is fine because I've enjoyed myself here. I don't even think about getting cut. It's happened to me twice in my career already and ti can drive you crazy thinking about it. There's nothing you can do if it's going to happen anyway, so why worry about it?

"I know I can play and, given the right opportunity, play well. I'm ready and willing to do whatever they want me to."

Bailey, 28, from Texas-El Paso, originally was drafted by the Houston Rockets on the second round in 1974. He played little in two seasons there and was traded to Atlanta.

The Hawks cut him the next season and he sat out the year. He then went to New Orleans as a free agent.

"I was a defensive specialist 12th man," Bailey said, "and sometimes I sat there for a month without playing."

He was cut by the Jazz and played last season for Reno of the Western League.

He led his team in assists and rebounding and was second in scoring. He guarded the opposition's top scorer, even if that player was a forward.

"I'm not a great scorer or anything like that, so I've concentrated on helping in any way I can," Bailey said. "I might get called on in the last 11 or 12 seconds, or for a whole game. If that's my job, then I'll do it and do my best because that's what the team needs."

The Bullets got a scare late in yesterday's practice when Chenier experienced difficulty breathing and had to leave the workout. After resting in the training room, Chenier recovered. "I was just short of breath," he said. "It was like an exhausted feeling. I'm okay. The last thing I need is to have people worry about me as much as they have the last two years."

Chenier was sent to the doctor as a precautionary measure and pronounced all right . . . The Celtics are the best shooting team in the league, making 52 percent of their field goal attempts . . . Bird is averaging 18.8 points, Dave Cowens 18.6 and four other Celtics, M. L. Carr, Cedric Maxwell, Tiny Archibald and Chris Ford, are averaging in double figures . . . After tonight's game the Bullets will be off until Friday when they host the San Antonio Spurs.