Mall monster and bargain behemoth, the giant so-called big-box retail store strides mightily these days across the American consumer landscape.

Costcos, Wal-Marts and Targets have served up such a potent mixture of low prices, bulk buying and product array--cereal, tires, vacuum cleaners--that they have even been memorialized in an episode of "Seinfeld."

Now comes the diminutive City of Rockville, already a vast land of merchandise, to say of the big box: Enough.

Though their numbers attest to their popularity, big-box stores also generate opposition from citizens and municipalities concerned about the huge, blank look of their architecture, and potential increases in traffic congestion.

On Monday night, the mayor and council unanimously passed a six-month moratorium that halts development of such projects until a study can be done, and plunges the city into the national debate on the issue.

Rockville, bisected by Rockville Pike--one of the busiest and at times most congested commercial boulevards in the area--has been trying for years to improve the traffic and aesthetics along the shopping-center-crammed pike.

Most recently, the city tried banning the sign walkers who pace the pike's sidewalks clad in advertising, but gave up after an outcry from small businesses and the sign walkers themselves.

Led by Mayor Rose G. Krasnow, a longtime opponent of such stores, Rockville enacted the big-box moratorium to "take a serious look" at the issue "and find out what the citizens of Rockville want."

The moratorium halts processing of city permits for single-use retail stores of 60,000 square feet or more until April 10. It was immediately assailed by property owner Ronald Cohen, who applied last week to construct, among other things, a Costco store on the site of the Congressional South Shopping Center.

Cohen, his developers and lawyers and Costco criticized the moratorium as drastic, unlawful, unnecessary and a business calamity. Cohen said he had shut down several stores in Congressional South to make way for the new development.

Big-box, also called "value retail" stores, are growing rapidly, according to a research memo prepared by the city's community planning development services unit.

Wal-Mart announced in 1997 that it planned to open 100 stores of 188,000 square feet each, and Target announced the same year that it planned to build 800 stores just in the Northeast.

Nationally, cities such as Fort Collins, Colo., established big-box moratoriums, followed by regulations on their development, according to the planning memo. Towns in Montana, California and Wyoming have also studied the issue.

"I do feel that it was really time to take a look at the impact of these stores and see if we can shape [appropriate] legislation," said Krasnow, who admits that she shops at a Costco in Gaithersburg.

"Aesthetically, they tend not to be attractive," she said. "I was just up in Baltimore last week and saw one up there that was horrible. It really was. . . . They do tend to generate a lot of traffic, in part because they're so popular."

She said she believes that Rockville Pike is nearing its traffic "saturation" point "in terms of people's willingness to shop there."

Plus, she said, "we have some real concerns about what happens when the big box goes away, and it will, because all of these retail trends come and go. It's very difficult to put another use in these buildings."

Cohen, Costco and the developers, though, argue the point.

Architecturally, the proposed 135,000-square-foot Costco in Rockville will avoid the classic big-box look, said Richard Reiman, a Bethesda-based spokesman for Cohen's development team. He said the store will be largely hidden behind a ring of other retail stores built around the site's perimeter.

In addition, Reiman says, studies show that big-box stores generate less traffic because customers shop less frequently.

"The mayor and council have not eliminated the traffic problem," he said. "They have created almost an instance where Cohen could be forced to go to an alternative . . . which would create probably 40 percent more traffic than the existing design with Costco."