An Institute of Medicine panel yesterday recommended that major structural changes in the National Institutes of Health be made "sparingly."

Noting that there has been considerable pressure in recent years to expand the number of NIH institutes to focus on diseases of current concern, the 15-member panel concluded that "NIH is now at a stage where there should be a presumption against additions at the institute level."

Its report is particularly timely, because President Reagan recently vetoed a bill that would have added two new institutes -- for nursing and arthritis research -- to the 11 institutes that now sponsor the bulk of the nation's biomedical research. Since 1970, there have been at least 23 proposals to create new NIH institutes, 13 of them through legislation.

But after an 18-month study requested by the Health and Human Services Department, the panel questioned such changes.

"Adding new institutes can fragment the scientific effort, diminish communication, make effective program coordination more difficult and add to administrative cost," said its chairman, Dr. James D. Ebert. Ebert is president of the Carnegie Institution of Washington and vice president of the National Academy of Sciences, the Institute of Medicine's parent body.

The panel suggested that major changes at the NIH should be made only after a "formal review process" and recommended that a new Health Science Board comprising six scientists and lay persons be created to help the HHS evaluate research needs.

The panel said, however, that more flexibility was needed within the NIH to implement research changes.

It urged that the NIH director be given more authority, including the power to establish a "discretionary fund" of up to 1 percent of the NIH budget to promote new research areas or to transfer up to half of 1 percent of the NIH budget across institute lines "in response to a public emergency" like the epidemic in acquired immune deficiency syndrome (AIDS) cases.

The various NIH institutes focus on diseases, organs, life stages and fields of science. The National Cancer Institute, with roughly one-fifth of the NIH's $5 billion budget, is the largest.

"The committee finds NIH in good health, and it wants to make sure it continues in good health," Ebert told a public meeting.

The panel suggested that proposed structural changes be subjected to several criteria: whether the mission is compatible with the NIH research mission and "not focused on regulation, health services, or other non-research activities;" whether the proposed area already receives adequate funding; whether there are good prospects for scientific growth and for sufficient funding and whether the change would, on balance, improve communication and management.

The panel did not examine the value of the two recent institute proposals. Ebert said he felt that they should undergo a new review. "It would provide a test of the proposed system," he said.

Panel member Adam Yarmolinsky, a Washington lawyer, noted afterward that political considerations are "inevitable.

"We're not recommending a substitution, we're recommending supplementary measures that will make [the process] better," he said.