Julie Dey stood in a hallway at Fairfax County's W. T. Woodson High School at 3 o'clock yesterday morning and cast an eye at 350 of her fellow suburbanites, some still wrapped in nightgowns and bathrobes.

"Oh, I was scared," said the 16-year-old Dey. "I just put on my clothes and got out of there fast as I could."

Some 150 families were roused in early morning darkness in Fairfax City's Comstock subdivision by police and firemen warning of a 300,000-gallon gasoline spill at the massive tank farm abutting the neighborhood.

Fire officials said the overflow was discovered after residents in the area reported a strong smell of gasoline and the sound of "gushing water." Firefighters said at one point the gasoline was two feet deep in a holding pond that contained the spill.

"You could smell the gas two miles away," said one fireman.

A spokesman for Amoco, Robert G. Valerie, said yesterday that the spill at the company's No. 5 tank was caused by human error. Valerie acknowledged, however, that terminal managers were aware that an alarm designed to warn of tank overflows had not been working for more than a month while the company awaited repair parts.

Asked if a working alarm might have prevented the spill -- which he said occurred when an operator neglected to redirect a Colonial Pipeline Co. shipment from a smaller tank to a larger one -- Valerie said, "It's a possibility."

There was an odd blend of fear and unflappability yesterday among the evacuees at Woodson, who live virtually in the shadow of the farm shared by Amoco and two other major oil distributors.

As Dey spoke to a reporter, two firemen walked by carrying cardboard boxes full of coffee cups. "No food?" asked Dey, clutching her throat dramatically. "Where's the food?"

Fire and police officials had discussed an evacuation plan with residents of Comstock in January, and Fire Chief Gene Daily was pleased with the way it went yesterday morning. "Smooth as silk," he said of the 20-minute maneuver in which residents were alerted by authorities going door-to-door. "All in all we're tickled to death we didn't have a fire."

Comstock homeowners, some of whom remembered being evacuated four years ago when an explosion and fire killed a truck driver and caused $1.5 million in damage at the plant, spent the five hours at Woodson dozing, walking their dogs and meeting neighbors.

"They really haven't been too much trouble," said Nancy Carrillo, speaking of the gray and white tanks that comprise the view to the north. "After that first incident [the 1977 fire] they said we wouldn't have that much trouble, but after this morning, I'm a little more nervous about what could happen. I'm not quite as confident as I was about it."

An 8-year-old boy walked up, his hands around a small shoebox. He wanted to show someone his pet chameleon, which he had brought from home when the family was evacuated. "He's got to be the only one who brought a pet chameleon," said his mother, Paula Skrable, her 14-month-old daughter sleeping fitfully in her arms. The hall was full of leashed dogs.

"You get used to it," said Ellen Pollack, explaining the neighborhood consensus on the tank farm -- which was around long before the Comstock development. "It's part of the scenery, it's quiet. You do have the feeling of insecurity that something could happen, but it's not like an immediate threat -- you don't have sleepless nights over it."

And the effect of the tank farm on property values in Comstock?

"The first thing we thought of when we first bought the house was the proximity to a potentially hazardous area," said Pollack. "When we bought they were in the high-60s. That was a year ago. The prices now are in the middle 90s."

"They say we live in tornado alley, too," said Carrillo, laughing nervously. "We've had two in this area -- one this past spring, one in 1977. It's scary to think about it. Sometimes you just don't.