IT'S A GRIM BUSINESS imagining the Washington area stripped of offices leased or owned by the Defense Department, but that's exactly what some regional officials are starting to contemplate. More than 100 buildings around the region are wholly or partly occupied by Defense employees (not to mention the Pentagon itself; all told, some 50,000 Defense employees toil in Northern Virginia alone). Since Sept. 11, 2001, efforts to reinforce security at those buildings have focused on operating procedures -- making it tougher to get into lobbies and garages, for instance. But new Defense Department building security standards, adopted without public input and scheduled to take effect in 2009, would go much further, requiring, among other things, much greater distances between buildings and curbs.

At the moment, virtually none of the department's office buildings comply with those standards, and many or most stand little chance of doing so by 2009. If Defense sticks with them, the result could be an exodus of Defense workers and offices, as well as defense contractors who service them, from the metropolitan core to far-flung military bases or leafy exurban sites. That would injure the region's economy -- and the notion that security requirements can coexist with smart urban planning. The Defense Department leases or owns fully a quarter of Arlington's office space, for example, and those offices have played an important role in Arlington's signal achievement of the last decade: the evolution of the dense, citified Ballston corridor, where pedestrians can stroll to shops, restaurants and pubs, all near Metro. By requiring greater setbacks, the Defense Department would stunt the development of such urban landscapes.

The Defense Department "doesn't have an interest in going back to Fort Apache, but we do have an interest in protecting our people," Ralph Newton, a Pentagon official, said last week at a forum sponsored by the National Capital Planning Commission and three other groups. Protecting Defense employees is critical, but it's worth putting the problem in some context. A State Department study before the Iraq war found that only a tiny portion of terrorist attacks worldwide between 1997 and 2002 were against military installations; businesses were far more frequent targets. And in the case of the most damaging of all terrorist acts on a military facility -- the Sept. 11 attack on the Pentagon -- setbacks didn't make the slightest difference. They may even have made the Pentagon an easier target.

After Sept. 11, the government prudently advised citizens to continue with their daily routines. By adopting more stringent security standards than those embraced by other agencies or the private sector, the Defense Department signals that it is preparing to change people's routines for them. We have seen security concerns interrupt pedestrian and traffic flows downtown, and the city has suffered for it. It would compound the damage to prompt a large-scale exodus of Defense workers and contractors from the inner suburbs, and in the process allow fears of terrorism to cut short the region's urban revitalization.