It started off as a joke. What would happen if Europeans, Japanese and OPEC-rich zillionaires decided to buy up everything they could get their hands on in the United States? But no one is laughing anymore.

The United States is now holding a garage sale for the rest of the world. I had't realized how serious it was until I met a friend of mine from Paris named Alain at the Pierre Hotel. We embraced, kissed on both cheeks and headed for the bar. Alain owns a grocery store in Paris and I assumed he was in the United States to replenish his shelves with Kellogg's Corn Flakes.

But when I asked about it he was uncertain. "I don't know whether to buy Kellogg's Corn Flakes or Post Toasties."

"They're both very good," I said. "Of course I also like a bowl of shredded wheat once in while."

"I don't want to buy a bowl. I want to buy the company."

"The company?"

"Of course," he chuckled. "Why do you think I am in the United States?"

He showed me the valise full of Eurodollars he was carrying.

"Don't they remind you of Kleenex?" he asked.

"What a thing to say about the American dollar, Alain!"

"That's what you Americans used to say about the French fran."

"It was a joke," I protested. "Can't you let bygones be bygones?"

"All right," Alain said agreeably. "You see those Japanese businessmen over there? I heard them talking in the elevator. The little fellow with the Nikon camera just bought some land in New York."

"How many feet?" I asked.

"I'm not sure. I think he said it was 60th Street to 83rd Street on Park Avenue. How many feet would that be?"

"Both sides of Park Avenue?" I asked.

"Of course. He had to protect himself from any Arabs moving across the street."

I ordered a rum and Coca-Cola.

"A Swiss friend of mine is thinking about buying the Coca-Cola Co. Do you think it's worth the trouble?" Alain asked.

"It's not a bad company if you like Atlanta. Of course, if he bought Pepsi-Cola he could live in Greenwich, Conn.," I said.

"He doesn't want to live over here," Alain said. "He just wants to own something so that when he comes on a pleasure trip he can say it was a business trip and deduct his expenses."

"I see," I said. "Were you thinking of buying anything besides an American cereal company?"

"Well, I'm not going out looking if that's what you mean. But if my wife takes a fancy to something, as she did the other day, I'm not going to tell her no."

"What did she want you to buy for the other day?"

"Central Park," he said.

"I didn't know it was for sale."

"Neither did I. The negotiations were very tricky. First, I bought up the New York subway system, very quietly, through a Nassau Island bank. Then I went to Mayor Koch and offered to give him back the subway system in exchange for the World Trade Center. He made the deal. I then went to the World Trade Center people and threatened to tear down both buildings and make a park out of it unless they could find something decent for me. They finally came up with Central Park."

"But Central Park doesn't produce any income," I said.

"Who needs income? The only reason we're buying over here is to get our money out of Europe."

"Now wait a minute, Alain. I don't understand this. You Europeans have been attacking the U.S. dollar for several years because you say you have no faith in it. Why put funds into America if you don't believe in our economy?"

"Because, dummy, the only safe country in the world for a foreigner to invest his money is in the United States," he replied.

Alain called for the check in the bar. As he signed it, he asked, "What's a decent tip for the waiter when you own the hotel?"