It had all of the makings of an old-fashioned carnival: a big yellow and white striped tent, voices blaring from loudspeakers, a sunny Saturday afternoon and hundreds of smiling people.

They had come to the Rock Creek Gardens condominium complex in Silver Spring for what they hope will be the deal of a lifetime: 278 unrenovated condominium apartments going for less than $40,000 each.

"It sounded like a fantastic opportunity," said Joyce Shirer of Silver Spring, who was among nearly 400 persons--some of whom camped out at the complex Friday night--waiting for their turn to talk with a salesman. "I'm a single person looking for a good tax break. I haven't seen real estate prices like this before."

"We've looked at the one- and two-bedroom models," said William and Lisa Marr of Riverdale. They were thinking to buy a second residence as an investment. "This kind of opportunity only comes along once in a blue moon. We thought we ought to take advantage of it. It's going to be a great hedge against inflation."

Renovated units in the Rock Creek Gardens development, at East West Highway and the northern edge of Rock Creek Park, have sold for as much as $90,000. But the La Vay Corp., the redevelopment firm that owns the units on sale yesterday, has hit financial hard times and announced that it must sell all 278 of the unrenovated apartments by Sunday night to remain solvent.

Television commercials announcing the quick sale began early last week and newspaper ads yesterday and today continue to tell how the 35-year-old one- and two-bedroom units can be bought at 17 1/2 per cent interest with 5 percent down for owners who will live there and 10 percent down for investors.

And the people came. Young couples, some pushing their babies in strollers, came with wide eyes and visions of buying a new home at a bargain price. Singles made new friends who might become neighbors. Small investors were trying to buy two or three units while the getting was good. By the end of the day, the line of newcomers still stretched down the block.

Mitchell Pastula, 57, of Bethesda had been number 115 in line and now was seated in a folding chair at one of a dozen long folding tables. A crumpled blank check peeked out of his inside jacket pocket.

"I came prepared to make a down payment," said Pastula. "I'm separated from my wife. But I plan to buy one for her so that she won't have to pay apartment rent. I figure whatever renovations the place needs ought to be right up my alley. I'm in plumbing and heating and I can get all of the materials I need at wholesale."

Mike Fishch of Potomac, a single lawyer, sat and waited for his name to be called by a salesmen for J.E. Robert Co., the sales agent for the project. "This has been a wonderful singles weekend for us," Fishch joked. "The prices certainly are better than I've seen anywhere else, but I still have some unanswered questions. But the rumors have been great."