Bjorn Borg, the 26-year-old, five-time Wimbledon champion who was scheduled to resume his competitive career in March, announced yesterday he is leaving championship tennis, saying he had lost his competitive desire.

Borg will continue to play exhibition matches, said his coach, Lennart Bergelin, who related the announcement made by Borg to members of the media following his exhibition matches in Thailand.

Bergelin said Borg would fulfill a contractual obligation by playing one more tournament on the Volvo Grand Prix circuit, at Monte Carlo during the first week of April. He then will play exhibitions in Seoul and in the Suntory Cup in Tokyo, a four-man round robin, according to Bob Kain, Borg's agent at International Management Group in New York. "That will be it for 1983," Kain said.

In an interview with Kvallposten, a newspaper in Malmo, Sweden, Borg said he had decided to cancel his comeback after a layoff of about 1 1/2 years from tournament competition.

"I have not got the right motivation," the paper quoted him as saying. "I cannot give 100 percent, and if I can not do that it would not be fair to myself to go on. Tennis has to be fun if you are to get to the top and I don't feel that way any more. That's why I quit."

Kain, who was attending the Volvo Masters tournament at Madison Square Garden, said Borg has not completely ruled out a return later.

"Retirement is too final," he said. "At age 26, he felt he had expended all the energy he has to go for No. 1."

Bergelin said Borg wanted more out of life than running 12 miles a day and practicing four hours daily.

"Bjorn doesn't have the fighting spirit to go on practicing four hours a day," Bergelin said. "We have been playing for three months, and he is in good shape, but he has the feeling that he doesn't have it."

Bergelin said that Borg had planned to make the announcement on his upcoming trip to the United States, but that persistent press reports in recent days had led him to call a Swedish journalist and make a statement now.

Kain said Borg is relieved the decision has been made. "It was gnawing at him."

Kain added, "He is in great shape. He is happy personally. This fall was tough. He was hoping to have that feeling again to work, practice four hours a day. He doesn't want to practice any more. He doesn't want to go out and lose in the fourth round or the quarters. He is an all-or-nothing kind of guy."

Borg has been semiretired for almost two years after losing the world's No. 1 ranking to John McEnroe. His last big victory came in June 1981, when he won his sixth French Open.

But a month later, he lost a classic Wimbledon final to McEnroe, reversing the result of a year earlier. In 1980, he beat McEnroe in five sets in what many consider one of the best matches ever played.

His career had one major disappointment--he never won a U.S. Open. He reached the final four times, losing to Jimmy Connors in 1976 and 1978 and to McEnroe in 1980 and 1981.

"He just doesn't want to play any more," Kain said of Borg. "He doesn't want to go after the effort to be No. 1."