Second opinions on the need for surgery help reduce the number of operations and save money if -- a vital "if" -- patients are required to seek the second opinion to collect on their health insurance.

This significant conclusion, important to containing rising health costs, was announced in New York yesterday by Dr. Eugene McCarthy of New York Hospital-Cornell Medical Center.

Second opinion programs are fast increasing in number, said McCarthy, overseer since 1972 of the nation's first major experiment in them. They are more needed than ever, he added, since the number of operations performed in the United States increased by an astonishing one-third in the 1970s "and we are going to have to use many methods, including second opinions, to control health costs."

McCarthy's view of second opinions differs sharply from one stated recently by Steven Sieverts, vice president of Greater New York Blue Cross-Blue Shield. His tentative view is that his group's second opinion program may be convincing more people than ever to have surgery, because the second opinion often reinforces the first. Temporarily, Sieverts says, this could cost the plan money rather than saving it, though "in the long run," it should prevent further illness and thus produce savings.

McCarthy said a major difference between his study and the New York Blue Cross experience is that Cornell's compulsory program covers 273,8000 persons who have had more than 7,000 second opinions since 1972, and "this permits a statistically sound conclusion."

The New York Blue Cross-Blue Shield program is voluntary, meaning the plan will pay for a second opinion but subscribers don't have to have it. Its recent survey covered 1,500 such opinions.

"In voluntary program all over, some we administer and many others," McCarthy said, "only a self-selected 1,2 or 3 percent use second opinions. That's not enough to reach a firm conclusion on how the program works, one way or the other."

Two major insurers, Prudential and Equitable, have begun offering employers health plans that include a compulsory second opinion before an elective operation is covered. The state of Massachusetts requires a second opinion before elective surgery for Medicaid recipients. Ford, General Motors and Chrysler all offer voluntary second opinions to Detriot-area employes.

But "we now feel," McCarthy said, "that we could target these programs at just six or seven much performed procedures -- like hysterectomies and knee, back, cataract and bunion surgery -- with a much more dramatic yield in operations not done and money saved."

Consistently, McCarthy reported:

About 18 percent of those required to get a second opinion (and about a third of those who aren't required to) are told they either don't need the surgery or should try other treatment instead.

The overwhelming majority of both groups in fact do not have the surgery -- the decision is always up to the patient. About half report receiving no treatment at all in the first year of follow-up.

Cost-benefit analysis shows that there were $2.63 in benefits for every $1 spent on the second opinions.

"There is one more benefit," McCarthy said. "When a second opinion program is started, there is usually a drop of 8 to 15 percent in surgical benefits paid -- just because of 'the sentinel effect,' the fact that doctors recommending surgery now know another doctor may be looking over their shoulder."