SEVERAL WEEKS ago, the stock market went into a panic when a man in Florida, who runs a private service for investors, called up 3,000 of his clients and told them to sell all their stock. The next morning, Wall Street was in a panic and everyone was selling. Apparently, thousands of sane, educated people, who handle billions of dollars of investments, got caught up in the selling fever at the same time. And people all over America started wondering, if one man could make so many bulls into bears overnight, whether the stock market was a safe investment.

Also, if one man could affect the stock market with one telephone call, what about the other markets -- particularly the real estate market, which everyone says is overinflated?

I have this nightmare that early one morning I am going to get a phone call from my real estate broker, Longworth, who says, "Sell your house right away. The price is going to tumble."

"But you told me two days ago it was going to go up!"

"Don't ask questions. I've been studying the classified ads and it's time to bail out."

I wake up my wife and say, "We have to sell the house."

"When?" she wants to know.

"Right now. I just got a call from Longworth and he says we have to sell immediately, or we'll lose our shirts. I'll go down into the basement and make a 'For Sale' sign. You clean up the house and repaint the kitchen.

"At 4 o'clock in the morning?"

"We have to move fast before other people in the neighborhood are tipped off."

I put on my bathrobe, and go down to the cellar and nail a piece of plywood onto a stake, and paint "For Sale" in large black letters.

My wife is on the ladder, painting the ceiling. "Hurry up," I tell her, "before it's too late."

"Where are we going to live if we sell the house?"

"Don't ask stupid questions. We've got to get rid of this place before the market collapses."

At 5 o'clock in the morning I'm driving the "For Sale" sign into the ground.

My neighbor Ewing hears me and comes out in his bathrobe. "What the hell are you doing?"

I say, "I'm only telling you this because I'm your friend. The real estate market is going to collapse as soon as the market opens this morning. I got it on the hot line from my broker, and he hasn't been wrong since I subscribed to his service."

Ewing says, "Thanks for telling me," and rushes back into his house to make a "For Sale" sign. Apparently, he tells Sullivan, who lives next door, and Sullivan is soon out nailing a "For Sale" sign on his door. A few minutes later, Symington has one on his house, and so do Cafritz, Connolly, Seigel and Winston.

Word sweeps like a brushfire through the neighborhood. The Tower Apartments, the Westchester and the Colonnade also put up "For Sale" signs, and by the time the real estate markets open in the morning, everyone is standing in front of his house or apartment building, waiting to sell. As each hour passes, every homeowner keeps lowering his price. Houses that people wouldn't have sold for $200,000 are now going for $125,000. Then they drop to $90,000, $80,000, $70,000. But there are still no takers. Guggenheim, in desperation, offers to sell me his house for $50,000, completely furnished, but I offer to sell him mine for $40,000, and he says he'll take it.

In my nightmare I move into a Holiday Inn and get a call from Longworth, who says, "Well, was I right or was I wrong?"

"You couldn't have been more right. I've never seen the real estate market in this town take a nose dive like this. I managed to sell out at $40,000."

"The reason I'm calling," Longworth says, is that I've just been studying the new indicators, and it's now time to buy real estate again."

I wake up my wife. "Get dressed. We have to go over and see Guggenheim about buying back our house."

"For how much?"

"If he subscribes to Longworth's service, we'll be lucky if he gives it to us for $200,000."