The girl stomped her foot. She tugged at her pleated navy blue skirt. She whined. Still, her mother was unbending: No, she could not wear the jeans she had stashed in the family car. She had to wear her uniform on the first day of school.

"It's ugly," said the pouting student, Mabatimije Otubu.

"It's not ugly," her mother, Helen, replied.

Mabatimije is no prep school student with no say in the matter. She goes to Gaithersburg Middle School, one of three Montgomery County public schools that, for the first time this year, are joining a national uniform trend.

And as Gaithersburg Middle School students poured from yellow school buses and minivans on the first day of school in Montgomery County, Mabatimije was not alone wearing navy blue or khaki bottoms and white or blue tops.

An unscientific survey of about 35 students disgorging from one bus showed about half were dressed remarkably alike. "I don't like it, but my mom says I have to wear it," said Jose Haros, a sixth-grader wearing pressed khakis and white shirt.

"It actually feels great wearing one," said Eva Carrero, her white Peter Pan collar peeking from under a black sweater. "I don't have to get frustrated thinking about what to wear in the morning."

The lunchtime view in the cafeteria showed about 300 of the school's 800 students arrived the first day in regulation colors.

The uniform turnout was sparse at Waters Landing Elementary School in Germantown and at Galway Elementary School: spots of blue and khaki in a technicolored sea of pinks, oranges, flowers, sports jerseys, and plaids.

"I see one maybe," said Waters Landing Principal Eva Wetten, poking her head into one third-grade classroom. "But I don't know if it's just chance. It is the fashion."

At Gaithersburg Middle School, Shawn Jackson, a seventh-grader, pronounced uniforms "dumb." When told his khaki pants and white shirt looked an awful lot like a uniform, he said: "I know. I'm on punishment. I hit some dude in the head with a slingshot over the summer."

He'd rather dress like his buddy, Devon White, who took great pains to show the Yankees insignia on the rear pocket of his impossibly baggy jeans. "Now this is cool."

But eighth-grader Preetam Reddy said he liked his navy blue shorts and white shirt because it eliminates comments like, "You don't have any name brands on. What's wrong with you?"

Aside from the decidedly mixed feelings about uniforms, the opening day of school went fairly smoothly, county officials said, with a record 131,000 students attending 189 schools, many of them with the construction dust just barely cleaned up.

But some new students ended up sitting in study halls after problems with the county's new $4 million student information system forced registrars to produce some schedules by hand.

Uniforms are catching on from Seattle to Philadelphia. Many schools in Prince George's County and the District have had uniform policies for years. Proponents say they reduce discipline and gang problems and promote school spirit.

But there are no gangs at Gaithersburg Middle School. And ever since the school embraced the Character Counts program to teach values, fights and suspensions have fallen way off.

So, why uniforms? Especially when policy as recently as two years ago held that Montgomery was the kind of school district that didn't "need" uniforms.

"Don't they wear uniforms at Eton?" said Gaithersburg Principal David Steinberg. "If it works to bind the community together and say, 'We have high standards for everyone,' why can't we do that, too? It sends a message that you dress up to go someplace important."

Steinberg embraced the idea of uniforms after a group of parents, sick of slinky midriff tops, baggy pants and revealing booty shorts, surveyed the community and found overwhelming support for the order and neatness of uniforms.

"It sets a tone, and it shows that students belong here," said parent Cristina Price. "There are a lot of places all over the world where public education doesn't mean a free for all."

Plus, she outfitted her two children in clothes for the entire year for $200.

But others remain unconvinced. "It's just not something I felt we've needed," said school board member Patricia O'Neill (Bethesda-Chevy Chase).

Linna Barnes, president of the Montgomery County Council of PTAs, said uniforms may be a sign of the times.

"It's about control," she said. "Uniforms are just like V-chips."

Some parents worry uniforms may connote schools gone "bad."

"I certainly wouldn't want a perception that Galway is a troubled school. That affects a lot of things, like real estate values," said Roberta Goldberg, a parent who sent her two sons to school in brightly striped polo shirts.

But back at Gaithersburg, Helen Otubu hopes the rules will be even stricter for her daughter next year.

"I don't like that she's wearing sneakers with her uniform," she said. "Maybe later they'll change and only allow brown or black shoes."

CAPTION: Andrew Potocko, 11, right foreground, is one of the Gaithersburg students in uniform.