Elvin Hayes was the first of the Washington Bullets to poke his head inside the gym door. Smiling but silent, he stared at K. C. Jones until the Bullets' fallen coach finally turned around.

"E," Jones shouted delighted and thus was begun his reunion with the team that broke his heart even though it didn't want to.

One by one, the Bullets filed up to Jones, who no longer dreams of championships but simply wants to help the young and innocent Milwaukee Bucks muddle through the long, long season.

The setting was cold, tiny practice gym that is the exact opposite of the Bullet's feelings toward Jones.

Phil Chenier kidded him about the wall he couldn't climb on TV's Superstars competition. Dave Bing gently patted his spreading middle. "I earned it," Jones said. "I earned it."

Dick Motta exchanged whatever pleasantries a coach can with the man whose job he took. Wes Unseld simply shook Jone's hand and waited for him to say something. By now, Jones was in too good a mood to let his normal taciturnity get in the way.

"You watch out for this Unseld," he laughingly told a promising Milwaukee forward named Junior Bridgeman. "He'll knock you flat. And don't think he's a nice guy just because he helps you back up."

The reunion went on like that for 15 or 20 minutes and yet, after it was over, Jones knew he would still feel funny when he watches the Bucks play the Bullets here Tuesday night.

"It was the same way the first time I coached against the Celtics," said Jones, who spent nine seasons in Boston's backcourt helping lay the foundation for a dynasty. "I thought I was on the on the wrong bench then and I'll probably think I'm on the wrong bench against the Bullets."

If he had had his druthers last spring, Jones would have accepted a new contract with the Bullets. But the team's management, after two straight years of playoff disasters, refused to give him a dotted line to sign.

In polite circles, it was said is contract had not been renewed. But what really happened was that he had been fired.

"That's the way it is in pro basketball," Jones says now. "That's the way it is in sports. It doesn't matter if I thought it was justified. It was what the owner wanted to do and that's that."

For a while, Jones thought he had been railroaded out of his job by the Washington press. "I've stopped feeling that," he says. "The newspapers didn't get me fired."

Far better suspects were his players, who seldom matched their glowing reputations when it counted. But Jones is not about to knock them, particularly after Unseld complained bitterly about his firing and the emotional Hayes threatened to quit.

"That was very gratifying," says Jones. "That's the type of people they are. They're good people."

With their sentiments to comfort him, the 44-year-old Jones retreated to his Columbia, Md., home with his wife and five children, and waited to see what job offers came in.

"I had a chance to be athletic director at a couple of schools," he says, "and a couple of businesses wanted me to be a sales rep. but there was nothing that I really wanted."

Nothing, that is, until Don Nelson, thrown into the Bucks' head coaching job when Larry Costello was fired, called on Thanksgiving to see if Jones would help him.

K. C.'s speciality is defense and mine is offense," says Nelson, who lost his four games as a solo act. "I thought it would be a beautiful relationship."

Jones got his wife's blessing "She knows my life is basketball," hw said and four days later he was in Milwaukee signing a one-year contract.

That committed him to a bachelor life of which he is not entirely fond. His drab one-room apartment in downtown Milwaukee is filled with rented furniture. "I should rent a cook, too," he said.

At practice today, his attire bore further testimony to his need for someone to look after him. Not only didn't his blue sweater go with his chocolate brown pants, but his shirt tail was sticking out beneath his sweater.

There is nothing wrong, however, with the job he is doing as Nelson's assistant. The two Celtics have installed Boston's open-center offense and pressing defense, and Jones has made a personal campaign of helping the Bucks' neophyte guards, Brian Winters and Quinn Buckner.

"K. C. doesn't say much," says Buckner, who played college ball for Indiana's volatile Bobby Knight, "but when he does, it's always worth listening to."

Typically, Jones does what he can to avoid meeting a compliment head on. "These are good kids," he says. "When I came here, they were 4-25 but they were hanging together. They weren't getting fidgety or bickering among themselves. That's when you know you couldn't have a good team."

The Bucks' Christmas party may have given Jones his best chance to thank them for accepting him. Unlimbering the lovely baritone voice that has made his famous in nightclubs around the league, he sang "You're Nobody Till Somebody Loves You."

He knows that from experience.