How do you save a county of 580,000 people from a nuclear attack? In the case of Montgomery County, you can either relocate them all to shelters that don't exist, or you can evacuate them to Virginia and West Virginia and hope there are no major traffic tie-ups.

Those were the two bad-news scenarios of Warren E. Isman, Montgomery County's director of fire and rescue service, as presented at a briefing for the County Council on emergency disaster preparedness. Isman's message was clear: In the event of a major nuclear disaster, there's not a lot the county can do.

The county is, in Isman's opinion, essentially unprepared and helpless, mostly because the federal government has grown lax in its nuclear planning efforts. Consider:

* The federal fallout shelter program has "fallen by the wayside," to the point where shelters in Montgomery, which used to be stocked with food and cots, are now unusable.

* The warning notification system is in disarray. Federal air raid sirens have about a 5 percent failure rate, Isman said, and the broken sirens cannot be repaired because the federal government doesn't have a contractor to fix them.

* The county's mini-crisis relocation plan sent to the state contained what Isman called "some great gaps," including the fact that sending county residents into Virginia would be a surprise to Virginia authorities.

* The only nuclear-proof county facility is the Fire and Rescue Communications Center in the basement of the county office building in Rockville, but that facility would house only 40 "essential personnel," which does not, incidentally, include members of the County Council.

* The only other public nuclear-proof facility is the federal government's secret communications center off Mt. Zion Road near Laytonsville, except nobody is supposed to know where it is.

* And all of the relocation plans are predicated on the enemy giving three days' notice of a nuclear attack.

In the absence of specific plans, council members could only respond to Isman's rather bleak prognosis with black humor. "Well, if the missiles are as accurate as the Russians claim they are, then we really needn't worry about anything," said council member William E. Hanna Jr.

The council ordered Isman to study the costs and options of the county preparing nuclear shelters.