First the goggles, pulled down snug over the eyes. Then the white helmet. Solemnly, 12 year old Bill Pataky climbed into his brilliant blue torpedo of a car and hunkered down for the trial run.

He snuggled in low, hunched his shoulders, jammed his chin into his chest, and yanked the cockpit cover down around his nose. "We're clear if you're ready," said the attendant. There was a muffled grunt from the vicinity of Bill Pataky, who had pretty much disappeared, and then the green flag whipped up and his streamlined All-American Soapbox Derby racer rolled off down Arlington's North 26th Street.

It was not bad, all in all, for a test. Brakes, steering, aereodynamics - all sound.

"In the last three years this is the shape the Grand Champions have had, so I decided it must be a good shape," said Bill, reasonably. The only thing left to worry about was the official course - a hill, Bill understood - hefty enough to unsettle the stomach.

The hill is out on Eastern and Varntum Streets NE, and on July 16 some 45 torpedo-bullet-and shoebox-shaped racers will roll down 950 feet of it for the 36th Metropolitan Washington Soapbox Derby. Junior and senior winners come away with $500 savings bonds, first place trophies, an all-expense paid week in an Akron, Ohio campsite, and the weighty honor of representing Washington in the nationals.

Four years ago the future looked bleak for the Soapbox Derby. The 14-year-old national winner, it was discovered, had cheated. His uncle admitted to having rigged up the nose of the car with an electro-magnetic device that jerked it forward when the metal starting gate was dropped.

The uncle was casual about it - "It is next to impossible for any 11-year-old boy or girl to build a racer that can win at Akron," he told newspapers - but the Derby's sponsors were apoplectic.

The Derby wavered, rent by scandal. Then the rules were completely rewritten and the whole thing sprang up anew, infused with a kind of post-Watergate moral zeal: All mechanisms to be visible, open for inspection. No cars to cost over $75 excluding wheels, axles, steering assembly, and paint. Adult participation limited to certain specific jobs, such as holding heavy components. No glass, automobile parts, fenders, or starting devices.

"What happened," said Sydnee Schwartz, director of this year's local Soapbox Derby, referring to the great 1973 debacle, "served as the force behind all this." Now it's back to the original point of the race, she said - to teach about woodworking, aerodynamics and the elation of winning on your own.

Schwartz built a soapbox car once, too, but she couldn't race it. They didn't allow girls. Now they do, and girls are cleaning up: national champion last year, and the year before that. The rule book diagrams Joan Ferdinand's 1976 first placed All-American Winner, a hot little streak with a 52-inch wheelbase, steel and pine wood axles, and "Joan" written in script along the headrest.

There are presumably still a few sexists around to sneer at this, but none of them showed up yesterday. Two of the trial racers, in fact, were a sister and brother from Calvert County - Julia Teresa Voegtli, 12, whose goes by the name of Gypsy, and her 14-year-old brother Ben. Gypsy's car will be a kind of glowing pink, with a rose, Ben's will be marine blue, and their 15-year-old brother is putting together a magnificently evil black Derby racer with orange shark's teeth painted down the sides.

The look had changed some over the years. Bill Pataky got his Derby inspiration from the faded snapshots of his father, also named Bill, who still remembers the homely little creation he raced in Madison Square Garden Bowl in 1938. "I never won a championship, but I won quite a few heats," said the elder Pataky, who lives in Bowie and works as a director of financial management for the Navy.

His son groped for a proper description of that 1938 racer. "Well," he said. He was trying to be charitable. "It looked kind of like, um, like steps in front of a house." His father said that was a pretty good description.