At least 7.8 million people worked for nonprofit organizations in 1985, and the nation's nonprofit work force is expected to reach 9.3 million by 1995, growing at a faster rate than the rest of the labor pool, according to a study in the July issue of the Labor Department's Monthly Labor Review.

Workers for nonprofit groups were concentrated in the service sector and had lower average pay than workers in similar for-profit businesses, probably because fewer nonprofit workers had full-time jobs, said the authors, Georgetown University sociologist Denis Johnston and Yale economist Gabriel Rudney.

Most employes of nonprofit organizations were women, and about 11 percent of them were black, roughly the same share as the labor force in general, the report said.

The study found that nonprofit workers were concentrated heavily in four groups of services.

About two-fifths were employed in schools and colleges, libraries, religious organizations, job-training and vocational education organizations, and various noncommercial research groups.

Hospitals employed another two-fifths of the nation's nonprofit workers. As in education, virtually all employes of hospitals worked for nonprofit organizations. About 12 percent were employed by health and child-care services, museums, art galleries and membership organizations.

The fourth group of nonprofit employes worked in industries where most businesses were for-profit firms, but there were some nonprofit groups. By far the most important of these was nursing and personal care, but some employes worked for nonprofits in broadcasting, securities and legal services, among others. About 6 percent of the employes of nonprofit organizations were employed in this fourth group.

The study, using figures derived from the 1980 Census and other statistical surveys, found that:

Although women constitute less than half the overall labor force, two thirds of the nonprofit work force was female. In nonprofit hospitals, 81 percent of the workers were women.

In education, one-third of workers in 1980 had not completed four years of high school, compared with only one-fourth in the overall labor force. But a quarter had four or more years of college, substantially more than for the overall labor force. This tendency toward extremes probably reflects the sharp differences in the types of work within the nonprofit labor force.

Workers in education and medicine and executives of nonprofit organizations are often highly educated, while most workers in child-care and low-level hospital jobs have little schooling.

In 1982, the average earnings of workers in selected nonprofit industries was $10,150, compared with $12,936 for workers in for-profit segments of the same industries. However, "this may be attributable in part to the larger amount of part-time workers in nonprofit organizations," the study said. Only half the workers in nonprofits worked full-time year round, compared with four-fifths for the labor force as a whole.

While average earnings in nonprofits were lower overall, in some segments they were higher than in the for-profit businesses. Those areas were research labs, skilled nursing homes, membership sports and recreation clubs, certain health and allied services, child-care and social services.