The global economy faces a collapse not equaled since the Great Depression of the 1930s if the major nations fail to take quick and drastic steps to cut the U.S. trade deficit and equivalent surpluses in Europe and Asia, 33 leading economic experts warned yesterday.

That danger, they said, was signaled by the stock market collapse around the world in October and by an earlier plunge of the U.S. bond market.

The economists' conclusions were contained in a report issued here by the Institute for International Economics and simultaneously published by eight other international research centers.

The economists said Americans would have to accept a sharp cutback in personal consumption in the years ahead so that more U.S.-made goods could be shipped abroad to reduce the trade deficit.

As this somber forecast was issued, the Reagan administration was nearing completion of its official estimates for economic growth next year, lowering its prediction by about 1 percentage point to reflect the impact of the October stock market collapse.

A group of administration economists at the sub-Cabinet level has compiled several predictions of inflation-adjusted growth for 1988 ranging from about 2.4 percent to about 2.7 percent, officials said, compared with a 3.5 percent forecast issued last August. The administration's biannual economic forecasts are closely watched as measures of the president's success in achieving his goals.

The three Cabinet members responsible for making the final recommendation to the president -- Treasury Secretary James A. Baker III, Budget Director James C. Miller III and chief White House economist Beryl W. Sprinkel -- will probably choose a figure within that range, the officials said. The forecast is expected to be released early next week.

Such a forecast wouldn't be far above the average estimate of private economists. The Blue Chip Economic Indicators, a widely used consensus of private forecasts, is currently projecting 2.0 percent growth for 1988.

Officials stressed that new developments could lead Baker, Miller and Sprinkel to choose a growth figure higher or lower than the range recommended by their top economists. They cited as one such development the recent slide in world oil prices, which they described as highly favorable.

In general, administration officials said, the economy presents a particularly confusing picture right now. "You're buffeted by diametrically opposed economic advice," one official said. "Anything you predict or do stands to be wrong, more than any time I can think of."

But the assessment of the group of 33 international economists, which included two Nobel award winners and former high-ranking government officials from the United States, Europe, Japan and Mexico, was unanimously grim.

Specifically, the economists warned that a new meeting of the Group of Seven finance ministers and central bankers -- reported likely to take place next month -- would be futile and even counterproductive "unless more decisive action is taken to correct existing imbalances at their roots."

They said the November agreement between the White House and Congress for an American budget reduction package was "grossly inadequate," and called for additional $40 billion deficit reductions in each of the next four years, designed to slice domestic demand by 1 to 1.5 percentage points in each of these years.

That step, "the most critical single requirement," would free up resources that would be used to expand exports, reversing the experience of the past four years, when gross national product was growing at about 2.5 percent but domestic demand was expanding by about 4 percent, sucking in imports, the report said.

Europe and Japan, meanwhile, should take steps that would boost their domestic demand by about the same amounts, notably to stimulate investment: "The {European} Community, as a group, could temporarily swing into external deficit for a period, reimporting some of the domestic savings that have flowed abroad so as to be able to finance the investment needed at home to reduce unemployment," the report said.

The United States' goal should be to cut its trade deficit by $150 billion to $200 billion by 1990 -- avoiding protectionist measures -- with corresponding surplus reductions of $70 billion to $100 billion for Japan, $50 billion to $70 billion for Europe and $30 billion for the newly industrializing nations (NICs) in Asia, particularly Taiwan and South Korea.

The report counseled against trying to stabilize exchange rates now, suggesting that it would merely be repeating what the economists regard as a mistake made at the Louvre Palace last February, when six of the seven major nations pledged to hold rates at "around {then} current levels."

If the suggested steps were taken, the economists predicted that the dollar would decline to about 115 yen and 1.45 West German marks.

But the report warned that if the major nations do not reduce international imbalances, the dollar "could fall a lot further, and attempts to prevent it from doing so would be fruitless."

Such a plunge -- "by increasing inflation in America and the threat of recession elsewhere, and further undermining confidence in the world's key currency -- could lead to a financial crisis and a serious world recession.

"Indeed, it is particularly because of these dangers that we believe the national measures described ... are so greatly in the interests of both the countries concerned, and the world economy as a whole," the report said.

Stephen Marris of the Institute for International Economics, one of the authors of the report, said that this "directly refutes the view of a number of American economists that all you need to do is to let the dollar go down. The important point in addition to that is that the group is saying that 'leaving it to the market' will lead to disaster."

Several of the participants in the study acknowledged at a Washington news conference that since it is unlikely that such major steps as steeper U.S. budget deficit reduction and a faster, simultaneous expansion in all leading European countries will be taken in time, the probability is that market forces -- including a further unwelcome decline in the dollar -- will bring on a recession.

"The main danger today is that failure to correct these {trade} imbalances could lead to a serious world recession," the report said.

C. Fred Bergsten, director of the institute, said European participants were especially vigorous in urging strong action by West Germany and other European countries to shrink their international surpluses.

"There was a strong feeling that West Germany has become a major brake on growth in Western Europe," said Marris, former economic adviser to the Organization for Economic Cooperation and Development. He said 80 percent of the increase in the West German trade surplus since 1983 has come at the expense of other European countries.

The economists, who met here Nov. 23 and 24, represented a range of political and ideological viewpoints, and included the two Nobel award winners -- Lawrence B. Klein of the University of Pennsylvania and Franco Modigliani of the Massachusetts Institute of Technology -- as well as a number of former high government officials.

Among the others were Marris; the dean of West German conservative economists, Herbert H. Giersch; former Japanese foreign minister Saburo Okita; Jesus Silva-Herzog, former minister of finance of Mexico; Rudolph Penner, former director of the Congressional Budget Office; Paul McCracken, chairman of the Nixon administration's Council of Economic Advisers; Richard O'Brien, chief economist of the American Express Bank in London; Rimmer de Vries, senior vice president, Morgan Guaranty Trust Co.; and Isamu Miyazaki, former vice minister of Japan's Economic Planning Agency.