Most of the nation's institutions for the aged and handicapped don't employ doctors on a regular basis, a government survey shows.

Only about two-fifths of the 23,608 homes for long term care of the elderly and disabled in the United States had a full-time or part-time physician on the premises in 1976, according to a new Census Bureau survey.

However, 84 percent of the institutions surveyed said they had outside doctors on call to take care of emergencies and other needs of residents who, in many cases, are confined to their beds or rooms because of physical or mental disabilities.

Rep. Claude Pepper (D-Fla.), chairman of the House Committee on Aging, said that even if correct, the figures show that medical attention for the institutionalized long term nursing home resident is grossly inadequate.

But Pepper also challenged the census figures as over optimistic and inflated on the number of doctors because they are based on questionaires the institutions can answer as they wish.

"I believe the report overstates the situation and gives the impression that there is more medical attention than there really is for nursing homes," Pepper said.

A Pepper aide said residents of nursing homes are in great need of rehabilitative medical attention in order to restore them to health sufficient to return to their own homes.

The survey showed that about 1.5 million persons were living in long term-care institutions in 1976 - about three-fifths of them women.

Nearly three-quarters of the entire 1.5 million long term-care resident were elderly people in nursing homes, where the median age was 80.

The others were younger people in psychiatric institutions, children's facilities or homes for the mentally and physically handicapped.

Stays at the long term-care institutions tended to be long and costly. More than half the residents stayed between one and nine years, and another 10 percent longer than one, all at a median monthly cost of $602.

A large portion of the burden for the institutions was paid by the federal and state governments. Medicaid - the government medical program for poor persons - was the main source of support for nearly two-fifths of the long term-care homes, and fees to residents and their relatives were the main sources for another two-fifths. Other sources were medicare, religious groups, charitable institutions and state and local government agencies.