The nation's leading cancer doctors have agreed to warn their often frantic patients that the much-publicized new drug, interferon, is far less impressive against cancer so far than they had hoped, and any good results have been very temporary.

"All the publicity about interferon is having the most unfair, most unfavorable impact on cancer patients we've seen in years," Dr. Charles Moertel, Mayo Clinic cancer chief, said in an interview.

"All over the country people are trying to buy interferon at any price. All the press, news magazine and TV reports have given them the idea it may help them."

A statement by the officers and directors of the American Society of Clinical Oncology says, "There is no evidence or even remote suggestion" yet to indicate that interferon may cure advanced cancer, and "no acceptable evidence" that it can extend patients' lives "regardless of the type or stage" of cancer they have.

The statement adds, "Many other new approaches to cancer treatment currently under investigation . . . have provided results equally or more favorable."

The leaders of the oncology society, an organization of the 2,700 specialists who treat cancer at major hospitals, agreed to issue the cautionary statement at their annual meeting in San Diego late last month. The final wording was reached in Rochester, Minn., Friday.

Interferon is a substance produced by the human body to fight infections. Though it has been available so far only in tiny quantities, some animal and human tests have offered hope that it may help combat infections and cancer.

"But we had reports at our meeting on its use in breast cancer, lung cancer and multiple myeloma, and it's also being tried in lymphomas," Moertel said. "In no case yet is there reason to move patients from treatments we know have some effectiveness."

For example, he said, in the best of three trials of interferon in breast cancer, there were only four positive responses in 19 patients, and the longest lasted 14 days.

Interferon has been tried in no more than 200 American patients so far. And its purity so far is low.

Interferon eventually may prove useful in treating cancer, "but the tests are still ahead," Moertel said. "At this point we really don't know what we've got, if anything.

"This is what we've trying to make clear to our patients. We want to tell them we've got a lot of solid treatments that should be tried before anyone goes into experimental approaches. Treatment is often very complicated. The best thing a patient can do is get in the hands of knowledgeable cancer specialists and let them call the shots."