The Boston Celtics became the fifth National Basketball Association team without a coach yesterday when Bill Fitch unexpectedly resigned in a hastily called press conference in the office of the team president and general manager, Red Auerbach, the man who hired him four seasons ago.

Auerbach said earlier this year that he would soon step down as general manager and owner Harry Mangurian said Tuesday that he was going to sell the team because of difficulties with Delaware North Corp., owners of the Boston Garden, where the Celtics play their home games. Kevin McHale is about to become a free agent and Larry Bird will become one at the end of next season.

All of this comes less than a month after the Celtics were swept by the Milwaukee Bucks in four straight in the Eastern Conference semifinals.

The Celtics gave no indication of a possible replacement, but speculation already has started that former Celtics player and coach Tom Heinsohn is in line for the job. Heinsohn was a candidate for the Houston job until negotiations broke off over salary two days ago.

Fitch was at odds with guard Tiny Archibald over playing time and had run-ins with a number of other players. He said the rumored player dissatisfaction and the team's performance in the playoffs had nothing to do with his resignation.

"If we had won the championship last night I'd feel better about the past, but I'd feel the same about the future," he said.

Fitch, 49, said he had no immediate plans and would not have resigned if Mangurian had decided to keep the team. He said Mangurian's sale announcement "was the back breaker" that convinced him to quit with three years left on his contract.

The Celtics join the Chicago Bulls, San Diego Clippers, New Jersey Nets and Houston Rockets in searching for a new head coach.