The Reagan administration is apparently getting ready to relax many of the health standards that a fifth of the country's hospitals must follow to receive Medicare and Medicaid funds.

Initially, the changes would apply only to what one official described as "the smallest of the small hospitals." But some critics fear the new regulations would be extended to other hospitals before too long.

The proposal would eliminate or relax rules affecting medical records and libraries, hospital kitchens, hospital governing boards and medical staff committees that monitor the results of surgery and medical care.

Some rules would be tightened and some would be added, however, including a requirement for hospital-wide "quality assurance," according to a proposal signed by Carolyne K. Davis, administrator of the Health Care Financing Administration in the Health and Human Services Department. The proposal is now being reviewed by the Office of Management and Budget, and, sources said, could be formally issued by HHS later this month.

The way the 102-page proposal reads, it would apply to all hospitals caring for Medicare and Medicaid patients. In fact, though, 5,200 of the 6,695 hospitals that receive the funds are inspected by the voluntary Joint Commission on Accreditation of Hospitals according to rules that generally are as strict or stricter than the federal regulations. The government accepts the JCAH's accreditation when it certifies a hospital to receive the federal funds.

The 1,495 non-accredited hospitals that would be affected immediately are mainly small, thinly staffed institutions in small towns and rural areas. About 1,000 have fewer than 50 beds. All told, they have only about 14 percent of the nation's hospital beds.

The changes, Davis maintained, would eliminate unnecessary, inflexible and "overly prescriptive" regulations without "adversely affect ing patient health and safety." She said the new approach would stress good "outcomes" rather than prescribing specific ways, such as certain committees, to get good results.

"The small hospitals can frankly benefit from some flexibility, given the tough fiscal times," another administration official said in an interview. But Davis' report conceded that savings would be "considerably smaller than $66,000 per hospital," with nationwide savings "less than $100 million."

Dr. Sidney Wolfe, head of the Health Research Group founded by Ralph Nader, said, "The millions of patients treated by these hospitals would indeed be at increased risk," and, beyond that, "the joint commission, seeing the federal government establish a double standard of care, might well weaken the standards for all hospitals."

Officials of the National Association of Social Work attacked a section of the proposal that would eliminate the requirement that hospitals that have a social work department must have a formally trained social worker. Here, too, they said, other hospitals beyond those affected could put less emphasis on social services.

Davis noted that criticism could be expected from other groups, such as dietitians who would be unhappy about the proposed relaxation of requirements for diet supervision and kitchens.

The changes were spurred both by a regulatory reform task force chaired by Vice President Bush and another named by HHS Secretary Richard S. Schweiker.

Among other things, the proposal would:

* Delete the requirement that affected hospitals maintain medical libraries, and that their medical staffs and governing bodies have specified rules and committees to ensure good care.

* Eliminate the requirement that the hospital administrator have formal training and credentials.

* Add requirements that the hospitals do "discharge planning" for patients who need further care, and that they must start being responsible for the quality of contracted services (such as radiology, pathology and even food service in many cases).

* Change present "standards" for five hospital services -- surgery, anesthesia, rehabilitation, respiratory care and infection control -- to "conditions," meaning "we could decertify the hospital if it didn't comply," said an administration official.