Bullet guard Phil Chenier participated in his first formal workout of the preseason yesterday but said his ailing back is not ready for the rigors of the NBA regular season.

"I'm still aiming to be ready for the season opener," Chenier said after practice. "But I don't know if I can make it or not." The Bullets open the season Oct. 21 against Detroit.

Chenier's return came on a day when coach Dick Motta said he had made up his mind about who will start at center this season. His choice: Wes Unseld.

"Wes has had an excellent preseason and I see no reason not to start him," said Motta. "But that doesn't mean Mitch Kupchak won't get plenty of playing time."

Motta reaffirmed that Kupchak, the their apparent to Unseld's spot, would play at least 30 minutes a game at forward and as Unseld's replacement.

"Mitch is so valuable to us coming off the bench," said Motta. "He can pick us up with his enthusiasm. He knows how we feel about him."

Motta was less specific about Chenier's immediate future.

"It's hard to tell what is going to happen with him," Motta said. "If he can get some game time in this week and work hard all next week, he should be O.K.

"Even if he misses playing this week but is close to being ready and can work next week, we probably can go with him as our third guard. We'll have to wait and see."

Chenier will not accompany the Bullets on a two-game swing through the south that starts tonight against the New Orleans Jazz in Little Rock, Ark. The same teams meet Wednesday in New Orleans before the Bullets return to Capital Centre Thursday for a game against the 76ers.They play Houston in Philadelphia Friday night to complete their exhibition game schedule.

With Tom Henderson (ankle) and Bob Dandrige (knee) also still hobling, Motta is having to use secondline players more than he normally would his far into the preseason. He hopes to have both ready for the 76ers.

Chenier said his back is better than it has been. "But I have to be careful out there." I don't have very much mobility right now."

Motta's choice of Unseld as his starter is based on two factors; the Bullet's offense and Kupchak's versatility.

Many of the Bullets' patterns depend on the ability of the center to set picks and screens, a role Unseld fills as well as anyone in the league. He also is tossing those marvelous outlet passes again, which Motta feels will enable the Bullets to regain their missing fast break.

"He's worked very hard in practice," said Motta. "I told him today that he is way ahead of where he was last year at this time. He's slimmer and he's responded to Kupchak's challenge."

Although Unseld says he is doing nothing different now "than I ever have in preseason," his actions indicate otherwise. He has run on his own after some practices and he asserted himself during workouts with his consistent physical play.

"Just think of the guy who has to defend these two guys," said Motta. "Wes leans on him and pushes him around and then Mitch comes in and pops from all over. It's a great one-two punch."

"I'd like Elvin (Hayes) to get about eight minutes of rest a game and Mitch will get those minutes," said Motta. "He'll get time at the other forward for Bobby Dandridge. And he'll replace Wes a lot."

Which Chenier and Henderson sidelined, Kevin Grevey will start at guard against the Jazz. He'll defend against Maravich. Grevey, who is playing well at his new spot, had to take on Doug Collins of the 76ers Saturday night in New York . . . . Motta said Joe Pace helped his cause considerably with his play in New York."We have to take a close look at him," said the coach . . . Dandridge's score knee is not responding to treatments as fast as the Bullets had hoped . . . . The 76ers aren't sure whether Julius Erving, who has a bad knee, will play Thursday night. He has not appeared in an exhibition game this season.