At Arlington's Claremont Elementary School, you can get a gallon of gasoline for 98 cents. Before you rush down there, be warned: The gasoline pump like the car it fuels, runs on the vivid imagination of 12-year-old Ellen Libey.

The cardboard pump is part of Ellen's design for a neighborhood. Other parts include high-rise apartment and school buildings with pedestrian crossways connecting them, an amphitheater (every neighborhood should have at least one) and a supermarket.

Ellen and 21 of her sixth-grade classmates who expressed an interest switched from a larger team-teaching program to work with Ted Kvell, a bearded, soft-spoken architect. Creating model neighborhoods in a four-week warm-up exercise, explains Kvell, a "laboratory for ideas in city design."

Stimulated by photos and discussion of futuristic design, the students combine practical conveniences like the neighborhood 7-11 with the needs of the future to create imaginative designs like:

A Habitat-style research center, complete with radar, made by 11-year-old Julie Hudson out of styrofoam squares.

A combination school (upstairs) and supermarket (downstairs) that serves two traingular apartment buildings with more than 40 floors each. Eleven-year-old creator Timmy Kinder says he doesn't live in an apartment himself. "That's why I like them." His co-architect, 12-year-old Shawn Wyatt, explains the triangular design: "It looks right."

A body shop that services human bodies, according to its 11-year-old creator, Linda Moss. "This is fairyland," she explains patiently, "and in fairyland most people walk, so their feet get tired. Robert Redford could come in here with tired feet, and in 10 minutes, we'd get him a new pair."

An underground city, designed by 11-year-old Michael Braxton and 12-year-old Cory Redick to avoid the "pollution that's taking over the world." Here, a subway system modeled from drinking straws runs to cardboard triangles stacked as high-rise, a school with a playground, several townhouses and, or course, the 7-11.

Once these "laboratories" are completed, Kvell and teacher Lynn Lupton will lead the class on to bigger things: designing an entire city. "The children will make all the choices," Kvell says, "where they want the city -- on land, under the sea or in space perhaps -- and whether they want it to be for now or the future.

The planning will begin with class discussions and essays on transportation ("especially for nondrivers, like children," Kvell points out), energy use, city growth and technology.

These decisions made, one group of children will draw up a set of architectural plans, while another group constructs and actual model. "What we hope to end up with are the same basics any city planner creates -- a book justifying the city's plan, a set of drawing and a model," Kvell says.

The architect, who takes time off from his commerical and residential planning at Kvell/Corcoran Architects to teach in Arlington's schools, finds his time with these Lilliputian designers to be an "excellent review of architectual basics -- they ask all those questions I haven't thought about since college."

His respect for teachers has also grown through the program: "I see what they face every day."

Teacher Lupton sees Kvell as "wonderfully flexible, and able to deal with the kinds of ups and downs you get with this age group."

She initially requested Kvell's assistance through Arlington's Humanities Program, a $44,000 project designed to bring professionals in the arts into the county's elementary and intermediate schools.

"We wanted the kids to be exposed to architecture, of course, but there are a lot of side benefits that go with having him in class," Lupton explains. a"For one thing, the kids are impressed by him -- he comes in here with a tie and a coat, and works in a real office downtown."

The children also get a weekly opportunity to work on a creative project, learn to work in a group situation and practice their writing and math skills. "Some of these kids have really opened up since starting this project," Lupton says.

Kvell concurs, citing "natural architect" Peter Campbell, a 13-year-old from Jamaica who brought his homeland's concepts of housing design to the project.

"Look at his buildings," Kvell says happily, "and his incredible attention to detail. The doors are rounded, the windows are decorated, each room is planned.

Is Campbell excited by the class? "Sure," he shurgs, while trying to apply a complex, curved roof to one of his houses. "It's a lot better than sitting around learning social stuides."