John M. Cavenagh, who established himself as a competent bureaucrat but never won the confidence of ambulance workers as director of the city's Emergency Ambulance Bureau, has told City Administrator Carol B. Thompson that he plans to resign.

Cavenagh's decision comes a few months after the city announced the service would be reorganized as of Oct. 1 and his job eliminated.

Under the reorganization, announced by Mayor Marion Barry in April, the ambulance service will be directed by a physician who specializes in emergency medicine and will again be folded into the fire department, with Fire Chief Ray Alfred as the bureau's overseer. Although it was clear that Cavenagh, 40, would no longer head the bureau, Alfred said at the time that Cavenagh might find another role.

A spokeswoman in Thompson's office said Cavenagh's resignation is effective Oct. 12. He then will become vice president of operations for the Delaware Valley division of U.S. HealthTec Inc., a private ambulance and emergency medical service that operates throughout Pennsylvania and New Jersey.

"I have worked very closely with Mr. Cavenagh . . . . He is the consummate professional," Thompson said yesterday in a statement. "Though quiet and low-key, he nevertheless provided committed, effective leadership for the ambulance bureau during one of its most turbulent periods."

Cavenagh took over in October 1987 during a period of severe staff shortages, frequent complaints of slow ambulance response times, and low morale among ambulance workers -- problems that still burden the service.

During his three years, Cavenagh gained a reputation as a bureaucrat "who knew all his numbers," in the words of one ambulance worker. But he never earned the confidence of many emergency medical technicians and paramedics, who said that he wasn't a fiery enough leader, and that he was detached from the problems of his workers.

Calvin Haupt, president of Local 3721 of the American Federation of Government Employees, which represents the city's ambulance workers, couldn't be reached yesterday, but in the past has been one of Cavenagh's harshest critics.

"The general feeling I get is that he's not sensitive to our worries and concerns," Haupt said in March.

Among members of the city's emergency medical network, Cavenagh was known as a good technician who brought small improvements to the system, but didn't possess the charisma or political savvy to overhaul it.

"I'm really sorry to see him go," said the director of emergency medicine at one local hospital. "He was a competent person. He was a very good technician, and he kept the system going. I think we're in deep trouble without him."