Dave Cowens wrote a message on the locker room blackboard before his first game as coach of the Boston Celtics.

"Win 23 of the next 36. Fifty percent (record) equals wild card."

Perhaps nothing quite sums up the dilemma of Cowens and Boston better than those scrawled words. The once-proud and powerful Celitics now must milk motivation from the prospects of a 41-41 season and the mere hint of a wild-card berth in the playoffs.

Cowens would like to rebuild the Celtics in the image of their former potent selves, when talk of a 41-41 record would have been considered disgraceful to the team's honor. And he only needs to look to the Washington Bullets, who play here tonight at 7:30 (WDCA-TV - 20), for a refresher course on how the old Celtics performed at least in two aspects of the game.

One is the fast break, which Boston employed as its principle weapon during its glory days. The Bullets now are the team with the splendid fast break; the Celtics have slowed to a walk even in the two straight games they have won under Cowens' control.

The other is role playing. On the great Boston teams, there were always a number of players who, on their own merit, would have had trouble lasting long enough in the NBA to collect a pension. But in a green-and-white uniform, folks like Jim Loscutoff, Tom Sanders, K. C. Jones and Don Chaney were transformed into semistars because they were never asked to do more than they were capable.

The Bullets now are a team of role players. Wes Unseld rebounds and passes, Elvin Hayes shoots and rebounds, Kevin Grevey supplies outside scoring, Tom Henderson runs the offense, Bob Dandridge does a bit of everything and the bench fulfills specific functions. If Washington develops a leak, coach Dick Motta has the proper plug to stop the torrent.

Cowens doesn't. Boston no longer has the bevy of superstars needed to carry less-talented teammates. For example, his big forward, Earl Williams, who played in Sweden last year, might have been successful with the old Celtics. But on this team, his liabilities are exposed for all to see.

It was Cowens who spoke up three years ago when Boston let a classic role player, rebounder Paul Silas, leave as a free agent. "We'll never be the same," Cowens said then, referring also to the earlier loss of defensive ace Chaney. "We need those players." He was right. The Celtics have steadily fallen apart the last two seasons.

Already, Cowens has talked about how his first priority as coach is "to talk to each player individually about his role and tell them what their role is.

"I'm looking for more sharpness. I want people to bust their butt more on defense and knock people down once in a while. I don't care if people get technicals or foul out if they are smart fouls. That goes for me, too.

"I definitely want more activity and enthusiasm. It makes a lot of difference when the bench is into a game."

How well another specific request "get our fast break going again" - is fullfilled probably will depend on Cowens the player.

Cowens last had one of those all-but, dive-on-the-floor, take-on-anyone Cowens seasons in 1975-76, when the Celtics won the NBA title. And he hadn't played well this season, save for one game, until he obtained his new title. Then he began hustling and Boston put together its mini winning streak.

Most of his teammates have never played alongside a perpetual-motion Cowens. Only four of the current 11 players were on the club even a year ago and, by then, the Boston dynasty was crumbling.

"A lot of us need our confidence back," said guard Nat Archibald, who has been inserted into to the starting lineup by Cowens. "I think our practices under Dave prove we can makes the effort. The guys have been putting out."

Cowens, a Huck Finn character who once drove a Boston cab to find out about life, is more predictable now. He got married seven months ago, is into health foods and nutrition and finds it easier to deal with his public life. But his restricted until General Manager Red Auerbach makes some personnel moves.

Until then, Cowens can only hope some of the past can rub off on his current club.