Jim O’Brien resigns, citing a philosophical difference with GM Danny Ainge.

WALTHAM, Mass. (AP) – Jim O’Brien quit as coach of the Boston Celtics on Tuesday, after half a season under new boss Danny Ainge, the team announced.

Ainge announced O’Brien’s departure at a news conference at the Celtics practice facility.

He said O’Brien told him he wanted to resign at a meeting Tuesday morning, one of their regularly scheduled sitdowns to discuss “philosophical differences” on running the team.

“The philosophical differences, I thought, were much smaller than Jim thought,” said Ainge, who was surprised by O’Brien’s decision.

Ainge said assistant coach John Carroll would take over for the rest of the season, while another assistant coach, Dick Harter, was let go.

Ainge said that he took a more long-term view of building the team, while O’Brien was more concerned with short-term results.

He said he was willing to work through the philosophical differences, but “Jim did not see that long-term vision that I saw.”

Ainge, who appeared at the news conference with one of the team’s owners, Wyc Grousbeck, was also trying to add more offense to the team, while O’Brien had always placed a heavy emphasis on defense.

“He was not sure he’s the man for that job … he didn’t want to take our money and our time under false pretenses,” Grousbeck said.

Ainge also said he had had differences with O’Brien over whether to play some of the older players on the team.

“We felt that there was a ceiling on the success of the old players … so we did not always agree on the players who should be on the court,” Ainge said.

A call placed to O’Brien’s agent, Lonnie Cooper, wasn’t immediately returned.

The Celtics are 22-24 after reaching the playoffs the past two seasons.

O’Brien’s resignation came one day after Byron Scott was fired as coach of the New Jersey Nets, the only team ahead of Boston in the Atlantic Division.

The Celtics lost five of their last seven games, including a 110-91 setback at New Jersey on Sunday. Boston trailed by 17 at halftime and sank just 36 percent of its shots for the game. In those last five losses, star Paul Pierce, who hasn’t gotten much offensive help, made just 27 percent of his shots.

Since taking over as director of basketball operations, Ainge has made numerous changes, trading Antoine Walker to Dallas before the season and Eric Williams and Tony Battie to Cleveland on Dec. 15. The first deal deprived the Celtics of a second scoring threat to go along with Pierce. The second took away two veteran leaders and keys to O’Brien’s defense-oriented approach.

Ainge, hired May 9, gave O’Brien a two-year contract extension running through the 2005-06 season. Before granting the extension, however, Ainge met with O’Brien and considered potential replacements among current college coaches, pro assistants, retired players and former NBA coaches.

O’Brien became coach when Rick Pitino resigned in January 2001. He took the Celtics to the Eastern Conference finals in 2002 and the conference semifinals in 2003. They lost both times to New Jersey.

The Celtics’ next game is at home on Wednesday night against the Detroit Pistons, who are second in the Central Division with a 29-16 record.

AP-ES-01-27-04 1851EST