Wayne Rosenthal of West Springfield had been trying to sell his 1977 baby-blue Oldsmobile Cutlass Supreme for weeks when he decided to try a new approach.

On a recent sunny Saturday afternoon, Rosenthal wheeled his automobile in one of the two fron rows in the parking lot at the Springfield Plaza Shopping Center in Fairfax County, stuck a "For Sale" sign on the window and positiioned himself for a deal.

"This is the hot spot," Rosenthal said, as he feverishly polished his car's trunk. "It's supposed to be a great place. I have a friend who bought a car here and he was satisfied."

For little more than a year now, Rosenthal and others have transformed the parking lot's front rows along Old Keene Mill Road into a used car bazaar that has infuriated the shopping center's merchants and delighted area residents seeking an inexpensive way to dispose of the family clunker. On weekends, the action at the parking lot can equal that of any commercial lot in the area.

"I'm looking for anything that runs . . . a gas-saver," said David Cordasco of Woodbridge on a recent weekend, as he and his two children peered inside a dark blue 1973 Subaru with a $650 sign attached to its rear window.

Just a few feet away, Nate Lissimore checked out another model.

"Why does this thing shake so?" Lissimore, a Ft. Belvoir Army technician asked 32-year-old Danny Smith, as they watched Smith's 1978 souped-up Plymouth Arrow whir.

"Oh, it just needs a tune-up," Smith said, adding that his car, which he wants to sell for $2,900, has "FM and AM" and urging, "Would you like to look inside?"

Smith is typical of Springfield Plaza's used-car salesmen: well schooled in hard-sell tactics, always eager to start their engines, ready to cite gas mileage statistics and assure a customer that he is looking at "the best buy on the lot."

The difference between Springfield Plaza and most auto lots is that Springfield lacks regular hours. On weekdays, most Springfield sellers bring their cars to the lot early in the morning and return to pick them up that night. They usually post their telephone numbers on the "For Sale" signs and await calls from potential buyers at home.

On weekends, however, the lot is crowded with sellers and would-be buyers.

Springfield Plaza businessman Charles Brakewell is not pleased at the hoopla in front of his beauty salon. "This is an infringement on our right to trade," he fumes. "We pay $10 to $12 a square foot for some of this space."

Gene Hollins, who represents Weaver Bros., Inc., property managers for the plaza, is equally unhappy. Hollins says that his company periodically has been towing away cars at the owner's expense, because the impromptu sales lot makes the shopping center look "tacky."

"It's just going to take some time to get them used to not using the lot out there to sell their cars," Hollins says. But not all of Springfield Plaza's business people are upset.

"I think it's neat," says Sam Stewart, owner of a nearby printing shop.

"I don't mind it, because it brings me business," echoes Jerry Corbin, 57, who runs a barbershop and a pizza parlor there. Corbin, in fact, does some wheeling and dealing on his own. His brown 1976 Toyota currently is on the lot, with a "For Sale" sign.

Dana Kauffman, an assistant to Springfield Supervisor Mrie Travesky, says that complaints about the Springfield lot have reached her office and have been referred to county zoning authorities, the shopping center's management, and the state Division of Motor Vehicles, which regulates auto sales in Virginia. Travesky was surprised at how successful the car sales on the lot have become.

"We were under the impression tht it was just a couple of cars," Kauffman explained. "We didn't know it was that big."