Mention fuel cells to Pedro De Jesus III, 17, a Wilson High School senior, and he will tell you that this futuristic energy source used on Space Shuttle flights is more efficient than batteries.

Go across town to Woodson High School, and LaVencia Sugars, also 17 and a senior, will tell you all about the dangers of gentamicin and other antibiotics used to treat urinary tract infections.

While their friends romped through the summer, De Jesus and Sugars commuted by public transportation from their homes to area research labs to study their pet projects. De Jesus worked at the Naval Research Laboratory in Bethesda and Sugars at the Walter Reed Army Institute on Georgia Avenue NW.

Their dedication paid off two weeks ago when they both won the grand prize at the 39th annual District of Columbia Science Fair held at Woodson, at 55th and Eads streets NE. De Jesus and Sugars will go on to compete in the International Science Fair, May 12-18, in Shreveport, La.

The victory was a repeat performance for De Jesus. He took the top honors at last year's fair for his earlier research on fuel cells, which are used on manned spacecraft to produce water and power. Sugars won first place last year for her initial research on gentamicin.

"I was really surprised," De Jesus said. "I was hopeful that I would win the grand prize again , but I wasn't really sure about it."

Sugars said, "I was excited and I was just happy and glad -- ecstatic, I guess you'd say."

De Jesus and Sugars were among hundreds of junior and senior high school students from the city's public and private schools who submitted 365 projects in 12 categories ranging from the behavioral sciences to space science, according to the fair's organizer, Mary B. Harbeck, supervising science director of the city's public schools.

The projects -- most of them in physics, engineering and chemistry -- were judged by 140 scientists, engineers and mathematicians who rated the projects on planning, data, conclusions and neatness, she added.

Even though De Jesus attends school in an upper-middle-class Northwest neighborhood, while Sugars is in class with students from middle- and lower-income families in far Northeast, both work hard, love science and have parents who help and encourage them.

De Jesus, the only child of an Internal Revenue Service agent and an elementary schoolteacher, said his parents helped him by shopping for supplies for his exhibit, and, "They push me when I get kind of lazy."

De Jesus, who has a 3.0 grade-point average, likes camping. He is a member of the Reserve Officer Training Corps and wants a career in the military as a computer engineer. He has been accepted at Virginia Military Institute but is still waiting for word from West Point, he said.

"I admire him De Jesus because he listens well and follows directions well, and I think that's one thing that makes him a winner," said Gladys Morgan, a science teacher at Wilson who worked closely with De Jesus on his project.

"He works hard and completes the job," she said.

De Jesus won the grand prize, an 11-by-14 inch plaque, for his expanded research on the fuel cell, a device that combines molecules of hydrogen and oxygen into drinking water with electricity as a byproduct.

A fuel cell failure shortened the November 1981 flight of the Space Shuttle Columbia.

The fuel cell is cleaner, more efficient and longer-lasting than conventional power sources such as batteries, but the cells need platinum to work best and that metal makes them too costly for widespread use, De Jesus said.

Last year he tried in vain to find a more economical substitute for platinum. This year, De Jesus conducted tests inside a fuel cell containing "p-benzoquinone," a greenish-orange crystal, to determine if different charges -- positive, negative and neutral -- affected the flow of current or the voltage in the fuel cell. He found that a difference in charge had no effect.

"It has no real application," De Jesus said about his experiment, "but somebody else might have some application. It's just research to find out what's going on."

Sugars, one of four children, is the daughter of a nurse's aide and a self-employed auto mechanic. "They my parents gave me moral support and gave me confidence," Sugars said. "They told me I could do it."

Outside of the laboratory, Sugars makes many of her clothes, sings, plays piano and likes to ski, camp and bike.

She wants to become a heart surgeon or a medical researcher and has been accepted at Georgetown University, Johns Hopkins and the University of Virginia, but she has not made a decision, she said.

Sugars received a plaque identical to De Jesus', but her project was very practical. It was to determine which antibiotics used to treat urinary tract infections had the fewest side effects.

Sugars divided 26 white rats into three groups. Then she injected one group with gentamicin, another with tobramycin and a third with amikacin. She analyzed the rats' urine and monitored their weight and water intake.

"LaVencia is an excellent, model student," said Alice Rier, a biology teacher at Woodson who assisted Sugars with the project. "The type of student that each teacher would like to have."

After two months of lab work, Sugars, who has a grade-point average of 4.0 (a perfect A), spent the next four months after school and on weekends, analyzing volumes of data, making graphs and charts and typing her findings.

"From my results, I concluded that gentamicin . . . was the most toxic, tobramycin was next and amikacin was the least toxic," Sugars said.

"The correlation it has with man is that a prolonged dosage of the antibiotics used in this study may lead to renal or kidney failure," Sugars added.

Grand award runners-up, who are eligible to attend the international fair in the absence of the winners, are Dunstan McMillen of Gonzaga and Brenda Wilkins of H.D. Woodson.

Senior High-First Place: Samuel Benn, Ballou; Matthew Costello, Gonzaga; Frederick Davy of Coolidge; Pedro De Jesus, Wilson; Teresa Doniger, Deal; Joseph McMahon, Gonzaga; Dunstan McMillan, Gonzaga; Darnese Pettway, Eliot; Luca Shavi, Gonzaga; LaVencia Sugars, H.D. Woodson; Brenda Wilkins, H.D. Woodson, and Ken F. Yu, Wilson.

Middle and Junior High -- First Place: Hung K. Cao, Deal; Sekou Coleman, Hardy; Carolyn Crone, Maret; Fergus Donaldson, Maret; Nicole Ferran, Maret; Patrick McGuinn, Maret; Alethia McNair, Rabaut; Andrew McPherson, Holy Trinity; Katy O'Connor of Blessed Sacrament; Edward Tom-Sahr, Jefferson; Karyn White, Jefferson, and Marcus Williams, Fletcher-Johnson.

The city's best elementary school science projects were judged in a special category at the science fair. Joshua Greenburg of Lafayette Elementary won first place.