In a get-tough effort pushed by "right-to-life" groups, the Reagan administration yesterday said it will issue new regulations to prevent hospitals from denying food and medical treatment to newborn infants with birth defects.

Hospitals that receive federal funds would have to post notices in delivery units and pediatric and intensive care nurseries stating that "discriminatory failure to feed and care for handicapped infants in this facility is prohibited by federal law."

The notices also would encourage use of a new 24-hour, toll-free hotline to report possible violations.

The announcement brought the government a step closer to monitoring the practice of medicine in the nation's hospitals.

An initial warning last spring had drawn sharp questioning from hospital groups, which argued that it interfered with the traditionally confidential medical relationships between hospitals, physicians and patients.

The new regulations follow the highly publicized death in Indiana last April of a 6-day-old boy known only as "Infant Doe."

The child's parents, backed by the family doctor and the state's highest court, allowed food and treatment to be withheld after the child was born with Down's syndrome, or mongolism, and other respiratory and digestive complications requiring major surgery.

Down's syndrome victims face varying degrees of mental retardation.

The case spawned a renewed national debate, and "right-to-life" activists took their complaints to the White House. On April 30, President Reagan directed the departments of Justice and Health and Human Services to apply civil rights regulations protecting the handicapped to the newborn. Last May, HHS warned the nation's nearly 7,000 hospitals that they could lose federal funds if they assisted in any efforts to "withhold treatment or nourishment discriminatorily."

The warning also held the hospitals responsible for the conduct of physicians and medical staff.

Acting HHS Secretary Thomas R. Donnelly Jr. said yesterday that the new regulations are intended to strengthen the administration's ability to deal with such cases. He said that HHS also will rely on help from state and local agencies "for speedy complaint investigations."

Privately, many medical experts believe that difficult life-and-death decisions involving newborn infants take place frequently in hospitals, but without the publicity given the Indiana case.

Since last May, according to HHS spokesman Claire del Real, the department has investigated "approximately five cases of alleged denial of treatment. None of the cases were resolved in the cutting off of funds because they were not found to have been in violation."

Yesterday, Gary Curran of the anti-abortion American Life Lobby charged that HHS "has been dragging its feet terribly on this thing" and said the new regulations came only after his group again brought the matter to the attention of the president.

"It took a rocket from the White House to get them to do anything," he said.

Curran warned that the new regulations are "only as good as the vigorous investigation and prosecution of cases of discrimation."

HHS spokesman del Real denied there had been any delays, saying "it takes a while to come up with the best solution."