Most afternoons, Nancy Carrillo knows exactly where to find her 11-year-old son Carlos -- kicking his soccer ball around the yard in back of the family's town house in Fairfax City.

Soccer is Carlos' passion, and every so often he sends a ball sailing over a six-foot-high chain-link fence on the back edge of the yard. For Carlos, the lost ball is no problem: He simply finds a gap under the fence and climbs through.

For Nancy Carrillo, lost soccer balls bring nothing but worries. On the other side of the barbed-wire-topped fence in the Fairfax Tank Farm, a 100-acre storage depot with 30 silver and white tanks that hold up to 5 million gallons each of highly flammable petroleum products. $ although Carrillo has learned to coexist with the massive steel tanks and the occasional smell of gasoline, she shudders when she thinks of the teen-agers who park and party on the driveway connecting Comstock and the back of the Fair City Mall, on the edge of the tank farm, 25 yards from her side door.

"If they really get smashed, they start throwing things at the tanks, and that's when it gets dangerous," she said.

Last Thursday, nearly 300,000 gallons of unleaded premium gasoline overflowed from a tank near the Carrillo home, forcing evacuation of the Carrillos and about 350 other people in the Comstock community at 2:40 a.m. City officials chose to evacuate only the first two rows of town houses closest to the plant, or one-third of the 250 homes in the community.

Although no fatalities or serious injuries were recorded in last week's accident, some families, especially those who had to be evacuated, are a little skittish.

"You go to sleep thinking any moment it could blow," said Carlos, whose bedroom window is only 50 yards from the nearest tank. "It's kind of weird dreaming the tank explodes and my windows cave in."

Four years ago a tank truck at the plant exploded, killing the driver. The explosion occurred when one tanker backfired and ignited gasoline that had spilled from another truck. The blast triggered a series of explosions that shook homes as far as a mile away and emptied nearby communities for three hours, city spokesman Thomas Wille said.

Carlos Carrillo was 7 when that accident occurred. "The flames were leaping as high as the tanks," he recalled. "My father got a beautiful slide from the kitchen window."

The Carrillos, like many families in the Comstock community, view the tank farm and the two accidents they have witnessed with an odd mix of devil-may-care abandon and newfound fear.

The 250 homes in Comstock, on the southeastern edge of Fairfax City, includes apartments, town houses and single-family homes south and west of the tank farm. Most of the community was built in 1975, 13 years after the tank farm. Four oil companies -- Citgo, Texaco, Gulf and Amoco -- use the storage depot. Last week's accident, as well as the one four years ago, involved Amoco equipment.

Herbert Jonas, and IRS agent who lives less than half a mile from the tank farm, didn't even know about the gasoline spill until he heard about it on the radio Thursday morning, several hours after it happened.

"I'm very fatalistic," said Jonas, 52, whose family was not evacuated. "My family was out in California in the San Fernando Valley when they had the earthquake in 1961. People panicked and packed their stuff and headed to Florida where they were wiped out by a hurricane. No matter where the hell you go, you're going to get hit with something."

Near Jonas' home last Saturday, the odor of gasoline was barely noticeable. Children were playing hide-and-seek around the brick town houses. Sprinklers were at work on lawns. A bicycle with training wheels sat in the middle of one sidewalk.

Strolling with his infant daughter Ashley in his arms, John Summers, a 33-year-old accountant, who lives on Main Street across from the Fair City Mall, said he rarely thinks about the nearby plant, except at night when tankers rumble by his bedroom window.

Closer to the plant, but still far enough away to avoid evacuation, Rick Kastens, a 29-year-old lobbyist, was trimming the grass in front of his town house where he lives with his wife Theana, 26.

"The only time we think about the tank farm is when something occurs," said Kastens, who has lived in Comstock four years. "I'm really not worried that it's a threat to me, and I really can't give you a logical reason why."

Approaching the plant, along roads like Bradwater Street and Wilcoxson Drive, the mood was a little different. Gusting winds were still thick with the odor of gasoline and white tanks were clearly visible over the roofs of compact town houses. Here, the people were not so nonchalant. These were the evacuees.

Tom Fisher, 20, lives with his mother and another person in a town house at 3859 Wilcoxson Dr., about a quarter mile from the tank farm. Along with his neighbors, he spent nearly four hours in a school cafeteria last Thursday.

Fisher had no trouble getting up and out in the middle of the night. His roommate woke him after he was roused by a fireman, and the two walked up the hill and across Main Street to join other neighbors at Woodson High School.

But his mother Joan, who happened to be staying with a friend in Springfield Wednesday night, is recovering from surgery and would have had trouble.

"The firemen wouldn't let us start our cars," said Fisher. "It's lucky my mother wasn't here. She walks with a cane because of her surgery."

Fisher said he couldn't smell gasoline Thursday morning, but after a heavy rain Friday turned winds from the tank farm to Comstock, the odor was overwhelming.

Amoco officials, backed up by assurances from local firefighters, contend the Comstocck residents can sleep easy, despite the two accidents in four years. Last week's spill was caused by a combination of human error and a faulty alarm system, they explained.

According to oil company representatives, the spill occurred after a worker failed to close a valve into a nearly full storage tank and open a valve to an empty one. Instead of flowing into a fresh tank, the 300,000 gallons of gasoline from the Colonial Pipeline continued pouring into the first tank, overflowed through a vent and onto the ground, where it drained into a rain pond at the southwest corner of the plant.

On Friday and Saturday, Amoco pumped gasoline from the pond and back into tanks. Fairfax fire trucks kept a 24-hour vigil, and residents were told not to light barbecues. By Friday evening, those restrictions were lifted and fire officials deemed the area safe.

Amoco officials said an electric switch that triggers an alarm whistle and a flashing light when gasoline reaches dangerous levels was not workinng on the overflowing tank. While every other tank has a working alarm, they said, parts for that particular tank have been on order for five weeks.

"As sorry as I am that the spill happened," said Amoco Supervisor Robert G. Valerie, "it's further proof that we can handle whatever happens at the farm with our personnel and do it safely and efficiently."

Fairfax City police and fire officials are investigating the spill. And some residents still are uneasy about the potential for disaster.

"Twice we've been lucky," said Terry Natale, 31, who lives with her two sons and a roommate at 3872 Wilcoxson, about 75 yards from the tank farm. "The way it's been operated, we're going to have a tragedy."

Natale, who can see the tanks from her kitchen window, said she would move if she could find a buyer. Most Comstock residents say their homes have risen in value from $60,000 to about $85,000 in the last four years.

"I don't think I'll find anyone crazy enough to buy this house," said Natale. "The prominent feeling here is let's make the best of it.

"I hope it's going to wear off and we can go on and live our lives."