A fallout shelter may protect you from a nuclear attack but it can't double as a tax shelter.

The Internal Revenue Service has a plan for staying in business in case the bomb drops, and the top priority would be collecting those taxes that would produce the most revenue. The agency does acknowledge that a nuclear attack likely would cause collections to suffer.Outlines of the plan were published in response to a directive from the Federal Emergency Management Agency to most government departments. The plan, dated Dec. 14, 1988, was buried in the Internal Revenue Manual, a voluminous document that guides IRS employees through every challenge from auditing a church to handling a menacing telephone caller.

"In the event of a national emergency (especially resulting from nuclear attack) the primary function of the Service is to support the secretary of the Treasury," the manual states. "This support as a minimum will consist of analyzing and reporting upon emergency tax legislation, prescribing regulations and forms, issuing rulings and technical information of an emergency nature."

Any money left after those tasks are performed would be spent on either preparing to resume full operations or concentrating on key functions of assessing and collecting taxes, enforcing the tax laws and handling taxpayer appeals.

Such essential functions would be resumed "when directed or 30 days after termination of the immediate post-attack period," the document says.

At that time, the manual states, IRS workers might find themselves facing strange new tasks, temporarily reassigned "to assure that the most essential functions are performed, regardless of and without any effect on the current positions or grades of the employees."

Officials in each area would weigh pertinent local conditions, consider the different types of taxes and taxable entities and concentrate "on collecting the taxes which will produce the greater revenue yield."

In many areas, it would be impossible to continue collecting delinquent accounts, the manual says. In those cases, the IRS would concentrate on collecting current taxes.

"However, in areas where the taxpaying potential is substantially unimpaired, enforced collection of delinquent accounts will be continued," the manual states.