First, the white helmet, secured tightly under the chin.

Then, solemnly, Bill Pataky walked over to the sleek black torpedo of a car. One leg at a time, he suqeezed his 5 foot, 6 inch frame into the 12-inch wide racer. Finally, the hood was lowered, concealing almost everything except Pataky's eyes, which were fixed on the track ahead.

This was it. The first public run of the Black Diamond III in nearly two years.

"Ready?" came the starter's voice.

"Ready," responded the muffled voice from deep inside the car.

As the gate dropped, Pataky's racer shot downhill.

The streamlined course, on 26th Street in Arlington, has been set up Saturday for the All-American Soap Box Derby trial runs.

There were no winners in Saturday's runs. Sponsors said the purpose was to give the kids a chance to practice before the first round of competition in July.

The test Saturday was not bad for a first run -- 15-year-old Pataky hugged the white line bisecting the course and the wheels spun at a reasonable speed. But this was cotton candy. The real jawbreaker -- the official course that Pataky missed last year because of construction holdups -- has yet to be tackled.

The official course -- a 950-foot roller coaster of a hill on Eastern Avenue and Varnum Street NE -- will be the site, July 12, of the 39th Metropolitan Washington Soap Box Derby. On that day, some 50 youngsters from the metropolitan area will snuggle into bullet and canoe-shaped roadsters to race one-on-one toward Derbydom -- the nationals at Akron, Ohio, in August.

Youngsters between the age of 10 and 15 who meet the contest rules can enter the metropolitan derby, which will send racers to the nationals -- the winner from the junior division and the winner from the senior division.

Seven years ago, scandal rocked the Soap Box Derby. The national winner of the "sport of children" had cheated. His uncle had installed an electromagnetic device in the car's nose that propelled it forward when the metal starting gate dropped.

The discovery, however, was secondary. Not only did the uncle admit the act, but he announced publicly what many persons had been quietly suggesting over the years -- that adult involvement in car construction had become an acceptable modus operandi.

It was obvious, the uncle explained, that the sophisticated design of most of the roadsters belied a hand other than that of a child.

Sponsors lined up to drop out. Attendance and participation dwindled.

Those days of scandal, said Sydnee Schwartz, director of the Arlington derby sponsored by the Downtown Jaycees, are a part of the past. New rules severely limiting adult participation and reducing costs has, Schwartz hopes, returned the Derby to its original goal -- teaching kids the thrill of accomplishing something on their own.

Speedsters 10 to 12 years old competing in the junior division must buy a car kit from the national organization and adult participation is limited to specific tasks such as installing steering and brakes.

Schwartz knows what it's like to operate under the old rules. She built a car more than 20 years ago, but was not allowed to race because she was a girl. Today, girls race the derby -- and win. Emblazoned across the last page of the official guide book are the names of the 1975 and 1976 national winners -- Karen Stead and Joan Ferdinand.

The presence of girls on the starting line seems to have had little effect on the participants. The sight of a pigtail peeking out from under a helmet during Saturday's trials seemed more interesting to the adults than to any of the young competitors.

"I've gone against a lot of girls," said 12-year-old Tom Hagan of Rockville, owner of The Rebel. "They've beaten me and I've beaten them. All I care about is whether they can race."

Can they race? "I've done it," beamed Jennifer Chisolm, a 12-year-old from Vienna as she sat in her black Jennifer's Special, "and I'm going to do it again."