A National Institutes of Health advisory panel yesterday made bold new recommendations for the drug treatment of breast cancer, endorsing for the first time a hormonal therapy with few side effects as a "treatment of choice" for many older women with regional spread of the disease.

"This is a major finding," said panel chairman Dr. John H. Glick, director of the University of Pennsylvania Cancer Center. Before this, he said, "there was no agreement, nationally or internationally, as to what constituted a standard of care for the postmenopausal woman" whose cancer is discovered in the breast and in nearby lymph nodes.

The 12-member panel specifically recommended the use of a hormone-blocking drug called tamoxifen for those women over 50 with breast cancer that has spread to the lymph nodes and seems dependent on the hormone estrogen to grow. Studies showed that in this group, hormone-blocking was effective in reducing the risk of death by about one-fifth -- down from 30 percent to 24 percent -- five years after initial diagnosis, Glick said.

Calling this the "first major endorsement of tamoxifen" in the United States, British tamoxifen researcher Dr. Michael Baum, a professor at King's College School of Medicine and Dentistry, called it a "revolution you've seen in the last few days" in acceptance here of hormonal therapy for older patients.

Rose Kushner, a consumer advocate and breast cancer patient who uses tamoxifen, estimated that about 36,000 older patients annually might be candidates for this hormonal therapy. "It's good news for postmenopausal women with locally advanced disease . . . . They will no longer be zapped indiscriminately with chemotherapy drugs that make them sick. Older women just can't handle the side effects as well as younger women."

But for patients under age 50, the NIH panel said there was strong evidence to support the use of more traditional cancer chemotherapy, using combinations of more toxic drugs, as "standard care." In this group, international studies found that use of such chemotherapy might reduce cancer deaths by one-fourth, from 36 percent to 27 percent in the five-year follow-up period.

"We've made progress. But we've got a long way to go," Glick said. He urged women to participate in continuing experimental studies to develop new and better drug therapies. He said the research to date has already made "significant advances" in demonstrating that "chemotherapy and hormonal therapy are effective treatments for breast cancer patients."

In 1985, there are expected to be about 120,000 new cases of breast cancer in the United States, and 38,000 deaths. About one in 11 American women will develop the disease some time in her life, with roughly three-fourths of cases in postmenopausal women.

Most breast cancer is detected in the earlier stages, but in roughly half of patients there may be evidence of some spread to adjacent lymph nodes, experts say.

"Despite advances in early diagnosis and primary treatment with surgery, radiation therapy or both, more than a third of these patients with cancer in earlier stages will develop systemic disease and ultimately die," the NIH panel noted in its statement.

Because of concern that hidden cancer cells may spread through the body and cause cancer at a distant site, most patients with lymph-node involvement are candidates for some form of "adjuvant," or follow-up, drug therapy, in addition to local removal of the tumor itself. But there has been considerable debate as to who should get which drug therapies, their value in preventing recurrences and prolonging survival, as well as the effect of the drugs on the quality of patients' lives.

The NIH panel of representatives from various fields of medicine as well as the general public met for 2 1/2 days to consider the evidence and develop a consensus on the best guidelines for tailoring drug therapy to patient groups.

The panel generally ruled out the use of adjuvant chemotherapy or hormonal drugs for women of any age whose cancer has not spread to nearby lymph nodes, but said there may be some "high-risk" exceptions.

In endorsing combined use of chemotherapeutic drugs for the younger women whose cancers have spread to lymph nodes under the arm, the panel noted that survival gains generally outweigh known side effects. It said although such drugs often produce temporary hair loss, nausea and vomiting, fatigue and lower white-blood-cell counts, such problems can often be controlled. The panel concluded that long-term side effects of the drugs are "extremely uncommon."

The antihormonal drug tamoxifen produces far fewer known side effects -- hot flashes and vaginal dryness -- but long-term follow-up studies are still under way. Sold under the trade name Nolvadex, the drug has thus far got Food and Drug Administration approval for use in more advanced cancer patients, but physicians have discretion to use drugs for other conditions.

Tamoxifen's potential value for postmenopausal breast cancer patients with lymph node involvement depends on the use of tests known as "hormone receptor assays" to show which cancers depend on hormones to grow.

Estimates suggest that more than two-thirds of older breast cancer patients may test positive. For those with positive lymph nodes and negative hormone receptors, the panel said standard chemotherapy may be considered instead but is not recommended routinely.