A BURST OF sound comes through the square box. It might possibly be a human voice. "That's another dealer asking if we have a door for a '74 Falcon," says Cordell Banks. In response to an incredulous look he explains, "You get so you know what's being said. It's inter-junkyard communication."

He is standing behind a four-walled counter stuffed with files, intercoms and automotive price lists. It's a typical Saturday for Cordell, a second-generation Banks at Banks Auto Parts. His father started the business 23 years ago, and it's now one of the biggest auto junkyards in the area.

What some might find an outpost of a technological society gone to seed is a treasure trove to others, and the car-part supplier of last resort to the desperate. In his Woodbridge, Va., lot Banks has more than 4,000 smashed vehicles spread in no particular order over 30 acres. Walking down the muddy lanes one can spot an occasional bus or remains of a moving van among the multicolored metallic display of what were formerly Cadillacs, Buicks, Mustangs and other driveway standards.

Banks is open Monday through Saturday, but Saturday, says Cordell, surveying the endless stream of customers --whose first words invariably are "Do you have . . ." -- is "people day."

WE GET TWO to three hundred customers in here on Saturday," he says. "During the week a lot of our business is answering requests from body shops or other junkyards." He excuses himself to tell one of his brothers, "At the end of the row near the Mustang is a '67 Lincoln with its fender missing. Bring back the bumper and front wheel." The Lincoln owner and his teen-age daughter look noticeably relieved.

The irony of the Banks' operation is that while their livelihood is machinery, they themselves use none in keeping tabs on their inventory. "I suppose we should have a computer, or some kind of system," laughs Cordell, "but we do it from memory." Since many a Banks has been initiated into the business while barely a teen-ager, it's not surprising that they know instantly where to find that '57 Chevy.

The typical Banks customer seems to be the dedicated and frugal do-it-yourselfer, with a healthy smattering of tinkering enthusiasts. "I'd rather spend $15 on a part than $100," says Ajit Gambhir, a turbaned maintenance worker living in Alexandria. He was waiting for the yard's Jim Walsh to dislodge a heater from a Plymouth Fury.

Dale City resident Bob Quinn, accompanied by his four-year-old son, was poking through the cars, ostensibly looking for "parts for a '69 Javelin. Actually, I was driving by and decided to stop in. I just like to look around."

Nineteen-year-old Donna Wheeler was toting a Volkswagen hubcap and looking for a battery for a Fury. She's a fairly regular customer. "I've always been mechanically inclined," she explains. "After some searching I usually find what I want."

OF COURSE, not everyone who enters the ramshackle Banks office is looking to save a few dollars replacing a dented fender. "One guy came in and told me he wanted to buy broken windshields, he didn't care how bad the condition was," says Cordell. "He bought about 20, all smashed up. He told us he was training himself to be a glass doctor.

"Lots of people want parts for sculpture and mobiles. One lady spent a day out here just taking abstract photos."

Then there are those who, while not budding Rodins, don't put the parts they buy back on the highway. "One guy from Springfield bought a wrecked Ford station wagon, mounted it on pontoons and made a car-boat," laughs Cordell.

Like most junkyard dealerships, Banks replenishes its stock largely through government and insurance auctions. "We've got a lot of police cars out there," he says. But they do get some cars from customers. "The individual sales run from someone paying us to haul away their car, to my paying $4,000 for a Mercedes," Cordell says. Occasionally a treasure rolls in that's not scavenged. Banks once got a '37 Cadillac and received calls from all over the country from prospective buyers. Another time a doctor and car buff from California, in Washington for a convention, drove out to Banks and left with a '54 Imperial.

Orlander Banks, Cordell's father, didn't start out in the junk business. Originally he had an auto repair shop, but after fixing a car he often found himself stuck with the vehicle when the owner couldn't pay him. He eventually decided to let other people fix the cars; he'd supply the wrecks. The business has moved four times and settled in Woodbridge in 1970.

THE SENIOR BANKS sits behind his own counter seven days a week, often flanked by his 14-year-old son, Kenny, and one of his daughters. He is a large, imposing man who claims he "never gets tired of working here." Mirroring the longevity of his own business, he is now supplying the sons and daughters of some customers. He also may be the only man in town who has a good word for one former government worker. "Bobby Baker comes in here. A real nice fellow. I sold him a radiator for his daughter's '67 Buick."

Cordell says he usually charges between 20 percent and half of the new list price for an auto part. But if a junkyard is the only place that has that widget that will get your chariot back on the road, price is a minimal consideration. "One guy had written to Detroit to get a piece for his Riviera. GM wrote back that they didn't manufacture it anymore, but told him to try us. Was he grateful when we came up with the part," says cordell.

Because it's a black-owned business, Cordell says the family feels an obligation to the black community. "We sponsor a whole bunch of football and Little League teams," he says pointing to their photos on the wall. "During the spring we often get about 20 of them trooping in to thank my father. He gets a big kick out of it."