Prevention is no free lunch, warns health economist Louise Russell. Bucking conventional wisdom, Russell, a senior fellow at the Brookings Institution, says preventative health efforts -- from immunization to exercise programs -- usually increase society's health care costs.

Not that such efforts aren't often worthwhile. But what makes them worthwhile, she says, is better health, not lower costs.

Preventive measures, no matter how beneficial, are rarely without risk and never without cost, argues Russell in her new book, "Is Prevention Better Than Cure?" (Brookings, $9.95 in paperback).

And if policymakers think prevention is going to stem the nation's increase in health care costs, Russell says they are bound for disillusionment.

"It's extremely unlikely," she says. "It's much more likely that it's going to add to medical expenditures . . . We're not getting it for free. We have to think about it as seriously as any other way we spend money.

"It's expensive to keep people healthy."

Russell, whose previous books include economic studies of medical technology and of the baby boom generation, undertook her latest book "because such incredible claims were being made for prevention." Often, she says, "uncritical thinking" about prevention oversimplifies complex health issues, exaggerates benefits and underestimates or ignores costs.

"First impressions about something as complicated as preventive care," she cautions, "can prove incomplete in important ways, or flatly wrong."

The U.S. surgeon general's report in 1979, "Healthy People," cited "an emerging consensus among scientists and the health community that the nation's health strategy must be dramatically recast to emphasize the prevention of disease."

And it is an article of faith among most doctors and public health officials that such a prevention-oriented strategy would not only improve health but would also save money in the long run. Russell rejects the second half of that claim.

"If the claims that prevention reduces medical costs are generally untrue, and the available evidence indicates they are, they may lead to an unwarranted disenchantment with prevention," she writes. "For even when prevention does not save money, it can be a worthwhile investment in better health, and this -- not cost saving -- is the criterion on which it should be judged."

Russell's book examines in detail the costs and benefits of several examples of preventive health strategies:

*Immunization. Even smallpox vaccination -- one of the great public health success stories -- was not risk-free. In 1968, when more than 14 million Americans were vaccinated against smallpox, there were nine deaths blamed on the vaccine and about 200 complications serious enough to require hospitalization. Although the vaccine was developed nearly 200 years ago, smallpox vaccination went through cycles of popularity and disenchantment, depending on the seriousness of outbreaks of the disease. The debate didn't end until the 1970s, when smallpox was finally eradicated and the vaccine literally "put itself out of business."

*Hypertension screening. Routine screening for high blood pressure is standard because of the potential serious consequences of hypertension -- stroke and heart disease. But a blood pressure check, which seems so easy and cheap on an individual basis, becomes costly when applied nationwide to millions of people, most of whom do not have high blood pressure. Careful studies have shown that the cumulative costs of screening, follow-up tests and long-term drug treatment for hypertension far exceed the medical costs of treating the consequences of undetected hypertension.

Whether such screening is worthwhile depends on the value of its health benefits, which in turn vary widely with group screened. One classic study looked at the cost of lowering diastolic blood pressure -- the lower half of the blood-pressure fraction, representing pressure between heartbeats. A reduction from 110 to 90 cost from $3,270 per year of healthy life in 20-year-old men to $16,330 per year for 60-year-old men. Life style changes. Besides its undeniable health benefits, exercise has "hidden costs" -- such as time -- that are often overlooked because they aren't paid for in cash. Exercise also entails risk of injury. One year-long study of 1,000 Atlanta runners showed that more than one third suffered injuries serious enough to force them to stop running for a while, and 15 percent were treated by a doctor for such injuries.

Russell urges policymakers "not to accept the easy generalizations" that prevention is both free and risk-free. In a time of limited resources, she says, preventive care should be no more immune to cost-benefit analysis than acute medical care is.

"We're not going to be able to do everything," Russell says. "We've begun to accept that for acute care. It's equally true for prevention."

Is prevention, then, better than cure?

"No blanket judgments are possible," Russell says. Preventive measures must be assessed on their own merits, case by case.

Measuring the cost-effectiveness of health programs -- for example, judging whether detecting and lowering high blood pressure is worth the cost and risk of screening and treating millions of Americans -- is extremely complex. But Russell says the current climate of limited resources offers a chance for such cost-effectiveness analysis, especially if economists can standardize their methods and assumptions so that policymakers can more easily compare the results of different studies.

In the end, decisions on the value of preventive measures depend largely on how the individuals involved tally up the benefits and costs. Russell, for example, estimates she spends at least two hours a week on exercise. Is it worth it?

After just a moment's hesitation, she delivers a circumspect answer worthy of an economist schooled in cost-benefit analysis:

"I think so."