BY LINDA ROSENSTOCK

It may come as a surprise to some that we don’t make health policy in this country based on portentous warnings from behind closed doors. There is actually a science to calculating risk. Making such sweeping decisions as President Bush has done on smallpox vaccination — keeping the public and experts in the dark — is simply indefensible.

The limited support of medical and public health professional organizations for the vaccination campaign may lead people to surmise, incorrectly, that the mainstream of expert opinion is behind the president.

In fact, public health experts involved in consultation on the recommendation — or those, like me, observing from outside the federal decision-making apparatus — might have come to a wholly different conclusion had the starting premise been a different one than “Assume there is a credible and small but finite risk of near-term intentional exposure.” In other words: “You health experts design a plan based on information we may or may not have but cannot share with you.”

This potentially false starting premise — and the implication that the risk now is sufficiently greater than it was before the Sept. 11 attacks to warrant a wholesale new approach to one of many potential biological hazards — takes on a life of its own.

The debate at the national level shifts from whether anyone should be vaccinated to who among those most “at risk” should be vaccinated and in what order.

And once on this slippery slope, the truly extraordinary recommendation emerges that all civilians be given the option to be vaccinated.

This particular recommendation reverses established public health policy: Once a clear public benefit exists, taking into account known risk — as with routine childhood immunizations — then the goal is universal coverage. And the smallpox vaccine will be provided to everyone free.

Would that the administration provide vaccines of known value such as for measles, mumps and rubella to the population at no cost. But that is a different discussion.

So is there anything prudent we can do to prepare for possible germ warfare?

Of course there is. First, the public deserves a clear explanation from the administration about the evidence of a threat. We deserve to know what they know.

If the risk is dramatically close to zero, as many of us in the health field believe, then a prudent course would be to continue as we are doing: working rapidly to manufacture a safer vaccine than now exists, to be available when and if the risk determination changes.

This is a credible course given the knowledge that smallpox does not spread as rapidly as many other infectious agents and there is a window of reasonable time (probably four days) when post-exposure vaccination is still effective.

If a credible, finite risk, even if small, can be convincingly established, then there will be honest disagreement among scientists and experts about the next best steps.

The debate will hinge on when to begin a vaccination campaign, before or after a documented case. And then the discussion, if we choose to proceed with pre-exposure vaccination, will rightly hinge on who should be vaccinated.

For now, we have not been provided with convincing evidence that any American should be.

Rosenstock is dean of the School of Public Health and was director of the National Institute for Occupational Safety and Health in the Clinton administration.