The death knell of the "big box" has sounded: They're banning them in Rockville.

You know the big-box store--its square bulk encased in a bland unnameable substance, possessing all the grace of a storage carton, beached in a vast ocean of asphalt--the toast of 1980s and 1990s merchandising.

It's over.

Nothing could make this clearer than for the City of Rockville to cry, "Enough!" Which it did one recent evening, when Mayor Rose Krasnow and Rockville's city council passed a six-month moratorium. They're going to "take a serious look" at the megastores, said the mayor, "and find out what the citizens of Rockville want."

Up to now, it has seemed that the goodcitizens of Rockville wanted more--always more--big boxes. At least it has seemed so to all who know Rockville mostly as a thoroughfare called Rockville Pike.

What Washington's serene mall is to monuments, Rockville's clogged pike is to the big box.

Krasnow said the pike is nearing its traffic "saturation" point "in terms of people's willingness to shop there"--thus proving herself the last elected official in America given to understatement. In our household, the person who journeys to Rockville Pike racks up big points on the family-sacrifices scale. I would happily take out the garbage for 52 weeks rather than navigate the pike.

The funniest part of Rockville's box moratorium is that developers proposing the newest box--a 135,000-square-foot Costco--said this one would be architecturally unobjectionable because it would be "largely hidden behind a ring of other retail stores." It's the perfect Rockville Pike aesthetic: Build enough awful boxes and more will be fine, because the older mammoths will hide them.

But now the fad is dying--and Rockville's glimpse of the light is not our only proof. Some planners are already puzzling over what to do with the box-filled malls and strips once we've moved on to the next trend. How we'll "recycle them," in the words of architect David Lewis, professor of urban studies at Carnegie Mellon University, is a challenge for the next century.

One hint: Here and there across the country, developers are beginning to convert some of the malls to more Main Street-like shopping areas.

Meanwhile, the real Main Streets are still succumbing to big boxism. One topic at the National Trust for Historic Preservation's huge gathering here recently was how to fight the big, suburblike buildings that drugstore chains are erecting on prominent downtown corners.

Preservationists showed horror-story slides: a noble 1906 U.S. Post Office building in DeKalb, Ill., torn down for a Walgreen's; an 1876 Friends Meeting house in Richmond, Ind., offed by a CVS. But they noted too that the chains have begun sometimes to do the nobler thing: to convert old buildings, as CVS has done here in historic Georgetown and in Lowell, Mass. Or to build new stores that come up to the sidewalk, have windows at the street level, use bricks like their neighbors and keep their parking out back. A new Rite Aid in Camden, Maine, looks like three classic New England buildings side by side; yet inside is the airy, spacious interior that the big chains want.

"If you accept standard, off-the-shelf, cookie-cutter design, you will get that every time. If you don't, you'll get better," Ed McMahon, director of land use programs at the Conservation Fund, told the National Trust folks.

Absent the pressure, though, the bad trends will persist. "Drugstores are building the last generation's retail buildings," said McMahon--though surveys show that 86 percent of respondents would rather shop in "a walkabout town center," and that such stores earn more than stores in strip developments.

For example, said McMahon, the big Barnes & Noble bookstore in downtown Bethesda, easily reached on foot or by bike, bus or subway, earned 15 percent more last year than the big Barnes & Noble on--you guessed it, Rockville Pike.

You can only wish Rockville's leaders the best in imagining the unimaginable--an other-than-boxlike future for Rockville Pike. But here is one heartening thought for them: Some future preservationist's fondest dream will be to take a Costco or Target and lovingly freeze it in time--an irreplaceable symbol of an era gone by.

For that monument, there can be no better site than Rockville Pike.