BALTIMORE, AUG. 31 -- In an experiment soon to be repeated elsewhere in the region, including the District, pupils at a public elementary school here began wearing uniforms to class today, a grass-roots project aimed at cutting costs for moderate-income parents and curbing social pressure among clothes-conscious children.

About 360 pupils, from prekindergarten toddlers to strapping fifth graders, showed up for opening day at South Baltimore's Cherry Hill Elementary School, most dressed in the new uniform: navy blue jumpers and blouses for the girls, blue slacks, dress shirts and ties for the boys.

The first of at least four schools in the area to attempt the idea, including Burrville Elementary School in far Northeast Washington, the Baltimore school is emulating the uniform code long in effect among Roman Catholic parochial schools and some private schools but traditionally shunned by public schools, with their broader-based enrollments and legal constraints in limiting personal freedoms.

The move comes after years of national concern over growing school ground competitiveness and clashes, some violent, among children vying for social acceptance in the volatile teen and preteen world of designer fashion.

Last spring in Prince George's County, a 17-year-old Fairmont Heights High School student was shot and wounded, apparently over a pair of $95 high-fashion sunglasses. The Burrville school is just across the District line from the Fairmount Heights section of Prince George's.

Although such violence rarely reaches down to the elementary school level, parents at Cherry Hill today repeatedly voiced impatience with what they say is increasing pressure from their children to buy expensive clothes, noting that poorer families often suffer shame when they cannot afford the outfits.

Uniforms should stop that, said Ronald Owens, uncle of 6-year-old Rodney Hicks at Cherry Hill. "The kids will be more or less on an equal basis."

Local and national school administrators say they do not know how many other public schools have adopted uniform programs, but the idea appears to be gaining momentum. In 1980, D.C. Mayor Marion Barry floated a standardized dress code proposal for the Washington school system, but the idea died.

Like Cherry Hill school, two other Baltimore elementary schools and Washington's Burrville Elementary will start their own uniform programs in the coming weeks. Burrville's program starts with the opening day of school in Washington next Tuesday. Boys will wear navy blue slacks and light blue shirts with ties. Girls will wear blue-and-gray plaid jumpers and blouses.

Burrville Principal Walter Henry said the school is in a relatively poor area of the city where it is often difficult for parents to purchase conventional school clothing.

"Many kids have low self-esteem," Henry said. "We hope {the uniforms} will help instill pride."

In Prince George's County, there are three "traditional academies" in the public school system where uniforms have been required for the past year. But the uniform is only one part of a broader magnet school concept with enhanced academic standards imposed by the county.

Cherry Hill, in contrast, developed its own "local home-grown program" independent of the Baltimore school system's central administration, said school uniform project president Jacqueline Powell.

"The parents in the community wanted it," she said of Cherry Hill, a scrappy enclave of mostly black low- and moderate-income families within sight of Baltimore's glittering Inner Harbor and central business district.

"It's been a very unifying thing," said Cherry Hill Principal William Howard, who with Powell surveyed the neighborhood on the uniform idea last spring and found widespread support.

In addition, Powell said, the program has generated a cottage industry of uniform making, with a local clothes designer and two seamstresses manufacturing the shirts, jumpers and slacks and a locally owned shoe store providing footwear at a 25 percent discount.

The price of a uniform: $30. Shoes: $18 to $20.

"When two pair of Calvin Klein jeans and a pair of Reebok tennis shoes costs $150," Powell said, "then it make sense to buy five whole uniforms for the same price."

Many children returning to Cherry Hill school today after the long summer vacation expressed acceptance, if not enthusiasm, with the new regime.

"It's okay," said Tiffany Wiley, a 7-year-old first grader, who, like her classmates, had swapped her jeans and sneakers for a pleated jumper and blue sandals and knee socks. "I like {the jumper} because it has buttons on it."

"I like the {blue} color" of the slacks, said 8-year-old Adrian Hughes, a third grader. His enthusiasm, however, did not extend to his necktie. "When you put it around your neck, it chokes you," he said.

Parents on hand for opening day showed almost unanimous approval.

"I love it," said Donna Hall, a family health care receptionist and mother of Cherry Hill students La Shawna and Da-Ron. "It's cheaper, you don't have to do all this shopping {for school clothes} and it cuts out all the competition over clothing."

"It's going to stop all this fighting over who's got this jacket and who's got that pair of pants," said Cynthia Keaton, mother of second grader Joseph Braxton.

Ten-year-old Dante Taylor, a Cherry Hill fifth grader, wasn't concerned about the cost but said his new uniform "looks good . . . . I wore white top Pumas and Jordache jeans last year . . . but these uniforms look better."

The origin of the uniform program goes back one year, said Powell, when she, Cherry Hill Principal Howard and others distributed fliers in the community and then held several public meetings to measure public acceptance.

"It was 90 percent positive," Powell said. Formal balloting among school parents later showed 97 percent approval, said Howard. "It was an idea that really caught hold and generated a lot of excitement," he said.

Next, the program received the blessing of the Baltimore school system's central administration, followed by selection of local clothes designer Jacqueline Britton to create and manufacture the uniforms.

A local shoe store offered to sell navy blue saddle shoes and other styles for a 25 percent discount, according to Powell. The final step, completed this summer, was to get all the children fitted.

Even with the relatively low prices, she said, a few Cherry Hill families could not afford the uniforms, and a modest uniform fund was established from charitable donations. Other families with several children who were unable to pay for all uniforms at once, she said, have been allowed to make weekly or monthly payments.

Howard said that since word slipped out last spring that Cherry Hill was going to uniforms, "I've gotten inquiries from principals and administrators all over the state."

Powell stressed that the uniforms are not mandatory, but said that 95 percent of the parents purchased uniforms and that the remaining 5 percent appear to have been delayed for various reasons or have ordered uniforms but cannot yet pay for them.

"The unity is what is so important," she said. "The people have come together. It's like a family."