The anxiety associated with returning to work after suffering from a mental illness is such that nearly three-fourths of employers responding to a recent survey said that reluctance to come back to work is the biggest obstacle these employees face.

''There's a stigma associated with these problems,'' said Colleen McMurray, senior consultant for William M. Mercer, which conducted the survey. ''People want to conceal them. They affect self-esteem. People are concerned with how they will be viewed when they return. These issues are all very real.''Indeed, according to the survey, 53 percent of employers contacted by Mercer claim to have more difficulty returning an employee to work following a behavioral health disability than after a physical disability.

Aside from the employees' reluctance to return to the job - cited by 74 percent of employers - other employer problems include:

* Uncertainty about how to create a supportive environment for the returning employee - cited by 30 percent.

* Uncertainty about wanting the employee back - cited by 24 percent.

* Supervisor resistance - cited by 23 percent.

* Concerns about liability - cited by 19 percent.

* Co-worker resistance - cited by 14 percent.

Unique challenges are posed right from the onset of the illness, said Ms. McMurray, who added that behavioral health is on the rise as a disability but remains difficult to diagnose.

''These types of problems are masked by concurrent physical problems that may underlie a behavioral health problem,'' she said. In other words, headaches, backaches and gastrointestinal disorders ''can all be a manifestation of a behavioral health problem,'' she said. ''Is the back problem the cause or the symptom?''

The changing nature of the workplace is partly to blame for the rise in these illnesses, Ms. McMurray said. ''Look at the things going on in organizations now: downsizings, reorganizations, more stress in the workplace, people having to do more with less, and layoffs in the ranks of the white-collar employees.''

Any employer who thinks these employees are more trouble than they're worth might take notice of the statistics by the National Mental Health Association, which maintains that one in four women and one in 10 men will suffer from clinical depression in the course of their lifetimes, she said.