Poseidon the gerbil is resting comfortably in his own self-sufficient underwater city, the end product of a program this summer to acquaint Hispanic students in Montgomery County with the demands and delights of engineering.

The tiny Atlantis was built in a physics classroom at the University of Maryland by 20 junior high school students whose activities were backed by a $20,000 grant from the National Aeronautics and Space Administration.

The city the students built lies submerged in a 70-gallon aquarium. It has a vegetable garden, a pint-sized heliport, skyscrapers, a runway and loading docks for boats from the "mainland."

It also has elevators to send food down to the city's lone occupant, but they aren't working yet. Poseidon is being fed by hand until the short in the elevator system is repaired. He no longer has free reign in his kingdom, however: The students had to put him in a cage when he began eating city hall.

For six weeks this summer, the 20 students also met with engineers, took field trips to scientific companies and museums, and took advanced courses in math and science.

"I learned more in six weeks than I would in a whole year of school," said Natalie Mendez, 13, of Rockville.

The program, "El Ingeniero" (Spanish for the engineer), began July 11 as a project of the Montgomery County Hispanic Coalition. It was put together by Lucy Negron-Evelyn; classroom space was arranged for by the university's Center for Minorities in Science and Engineering.

The idea for the program grew out of the concern of local Hispanic leaders about the small number of Hispanics choosing careers in engineering.

"We have a tendency to think of ourselves as poets, baseball players and lovers, but not engineers," said Orlando A. Gutierrez, Hispanic employment program director at NASA headquarters in Washington.

Ivan Vera, a graduate engineering student at George Washington University who was El Ingeniero's instructor, said the program was designed to give the 13- and 14-year-olds experience with typical problems.

"They were faced with the normal constraints: time, resources, technology and money," Vera said.

With those limitations in mind, the students decided on the underwater project, which they dubbed "Libertad" (freedom). The gerbil was placed in the city to prove it would support life.

The students divided themselves into four groups of engineers--oceanographic, civil, environmental and electrical--and worked together to meet their deadline. "I gave them recommendations, but sometimes they said no," said Vera. "I still can't believe how creative they were."

When the students discovered the airtight city they had constructed floated, Vera said, they placed buckets of water in the structure until it settled on the bottom of the tank. By weighing those buckets they determined that 110 pounds of lead weights had to be fastened to the city.

"They talked to us in an adult fashion. In our age group, we like that," said Evette Vasquez, 13, of Silver Spring. Maria Laborde, 13, of Gaithersburg, who kept a notebook that is being included in the final report to NASA, said: "I couldn't have spent my summer any better way. I've always wanted to be an engineer because I enjoy challenges."

The program ended last week, but the students have a special invitation from NASA to meet Franklin Ramon Chang Diaz, the nation's first Hispanic astronaut.

And Poseidon isn't going to bow out. Starting next week, he and his underwater city will go on display at the Montgomery County Science, Math and Computer Center at the former Connecticut Park Elementary School at 12518 Greenly Dr., Silver Spring.