While stock markets tumbled in a world-circling chain reaction yesterday, business leaders, economists and politicians in the United States responded with bewilderment, nervous joking, resignation and warnings that proof has now arrived that the U.S. economy needs tough decisions to turn it around.

Many corporate leaders contacted by The Washington Post declined to comment. Those who did respond sometimes said they simply didn't know what was happening. "We don't know how to interpret it and we don't think anyone else does either," said John Rolls, chief financial officer of United Technologies Corp., through a spokesman.

Others called the marketplace turmoil a predictable result of the United States living beyond its means. "This isn't a correction anymore," said Chrysler Chairman Lee Iaccoca in a statement issued by the company. "It's a board right between the eyes that had better wake us all up to the simple fact that we can't keep romping forever on borrowed money.

"The budget and trade deficits are the culprits," Iaccoca said. "The way to avoid panic is for the president to say, the binge is over. The president and the leaders in Congress have to lock themselves in a room and not come out until they take spending down and revenues up. The borrowing has to stop."

Richard D. Simmons, president of The Washington Post Co., said he was "as confused as anyone else." But he suggested that a major cause was common-sense principles being ignored. "For some time, the financial markets have acted as if the basic laws of economics have become inoperative," he said.

Economist John Kenneth Galbraith called the panic "reasonably predictable." He blamed it on two forces: large numbers of speculators and "economic misadventures" by the Reagan administration.

"There's one more thing that is predictable," Galbraith said by phone from his office at Harvard University. "After the 1929 crash, everybody in Washington rushed to say the economy was fundamentally sound. There will be a flood of similar comments in the next few days. And everybody should note their great historical value."

The U.S. Chamber of Commerce, meanwhile, offered a basically upbeat assessment. "The phenomenal selloff in the stock market is very likely to have run its course," the chamber's statement said.

Chamber President Richard L. Lesher was quoted as saying "there is very little likelihood of a downturn in the economy. In fact, because of the tax-rate reduction which will become effective in January 1988, next year will be a much stronger year for the economy than 1987 -- unless Congress decides to raise taxes."

David T. Kearns, chairman of Xerox Corp., also expressed hopes. "U.S. business in general is fundamentally strong," he said yesterday through a spokesman. "Corporate earnings reports are good."

And similar sentiments came from Mark Olson, president of the American Bankers Association. "The underlying basis of the economy is still strong," he said at an association meeting in Dallas yesterday. However, he said that the twin deficits, budget and trade, will continue to cause concern.

Members of Congress also expressed dismay with the day's fall. Many Democrats laid blame on the Reagan administration's economic policies. "You cannot continue to go forward on a spend, spend-borrow, borrow mentality," said House Budget Committee Chairman William H. Gray III (D-Pa.).

Democrats took particular offense at suggestions over the weekend by administration officials that Democratic tax-increase proposals had helped to touch off the panic, which began late last week.

"The administration is now blaming Congress," said Sen. Lloyd Bentsen (D-Tex.), chairman of the Senate Finance Committee.

"Last week they were blaming the Germans for raising the interest rates, and the week before they were blaming the Japanese for not expanding their economy," Bentsen said.

"But they {the administration} have failed to address either the budget deficit or the trade deficit or to have an energy policy that would make us more self-sufficient," Bentsen said.

"It's just critical that the president and the Congress sit down together and make the hard choices in the way of what has to be cut in the way of spending and what taxes have to be restored."

Staff writer Kathleen Day contributed to this report.