A longtime employe at the D.C. Department of Human Services has been suspended for 10 days without pay after writing the mayor and several other officials with complaints that his office is mismanaged and unprofessional.

The office "continues to allow employers to work part time for full-time pay," Benjamin H. Johnson III complained last June in a letter to Mayor Marion Barry that he mailed to several other city officials and distributed throughout the Human Services building. Instead of working, Johnson wrote, some employes went in late to the office, tied up the telephones with personal calls, played radios, read newspapers, took naps and spent too much time "visiting and socializing."

A social service representative with the agency's Income Maintenance Administration, Johnson, 51, has frequently written city and federal officials with allegations of waste and incompetence in his office. His outspoken comments almost got him fired once, and his latest letter is being called "discourteous treatment" to agency employes.

Johnson is appealing his suspension, but agency officials say they have lost patience with his penchant for airing his grievances so publicly.

"He's sending copies to the world," said Audrey Rowe, the city's commissioner of social services, who suspended Johnson. She said an in-house investigation and unannounced site visits failed to substantiate any of the allegations in his June letter.

A woman supervisor he accused of being repeatedly tardy, for example, had permission to come in late and work late because of child care arrangements, according to Rowe. A clerk accused of taking daily naps had permission to take rest breaks because she is pregnant.

While acknowledging past problems in the income maintenance office, which administers the Aid to Families With Dependent Children program, Rowe said employes have been working hard and making improvements. "Mr. Johnson should present proof or, if he's so unhappy, should go work someplace else," said Rowe.

Johnson, a 20-year city employe, came close to being fired for insubordination in 1977 until a senior government official intervened. In those days, his letters alleged "waste, inefficiency and incompetence" in the agency.

"I've been writing for 11 years," said Johnson. "I guess I average a letter every six months."