The stock market's plunge, which has wiped out about $850 billion worth of wealth since August, will slow economic growth in 1988 if not reversed, and a further decline could lead to a recession, a number of prominent economists and analysts said yesterday.

Consumer spending and business investment likely will be depressed by the decline in wealth caused by the market's fall and an undermining of public confidence, they said.

Just how big the impact is will depend on the future course of the stock market, the extent to which confidence in the economic future has been shaken and the actions of government policy makers. The economists and analysts called on the Federal Reserve to take whatever steps are necessary to provide enough money to keep the economy operating smoothly.

Before the market opened yesterday, Fed Chairman Alan Greenspan issued a statement saying, "The Federal Reserve, consistent with its responsibilities as the nation's central bank, affirmed today its readiness to serve as a source of liquidity to support the economic and financial system."

Consumer confidence, the pivotal factor driving trillions of dollars of individual spending decisions, appeared wounded by the market plunge -- but in a limited way. A Washington Post-ABC News poll taken Monday night showed that 37 percent of those questioned said the fall in stock prices means that "the United States is going into an economic downturn." But 58 percent said the dramatic decline in the market did not mean the economy was going to suffer a severe drop.

Even before Monday's slump, another Washington Post-ABC News poll had shown that 47 percent of those questioned said the economy is getting worse, a nine-point increase since June and the highest negative rating since December 1982, at the end of the last recession.

"Clearly a stock market crash of this magnitude results in lower spending levels throughout the economy," said Bernard Campbell, consumer economist at Data Resources Inc. "There's no question we think it will be a poorer Christmas season than we thought three days ago."

"The spending boom has been put in jeopardy," said Richard Curtin, director of consumer surveys at Michigan's Survey Research Center.

Whether the loss of confidence will snowball into a major contraction of consumer spending remains unclear. But analysts of consumer confidence emphasized that while fewer than 20 percent of American households invest in the stock market, many more feel their fates are intertwined with it.

"It's hard to say {the crash} represents a bigger concern for the wealthy investor who lost 20 percent of his stock value yesterday than for a lower income family that feels its job threatened," Curtin said. "It's very clear to many factory workers that trends in the overall economy affect their job security."

In addition, millions of other Americans depend on the market for the health of their pension and retirement plans. The Washington Post -- ABC News poll indicated that 70 percent of the respondents said they did not think their pensions would be affected by the downturn in the market, while about 25 percent did think so. Of the $500 billion held in private pension funds as of June 30, 40 percent was invested in the stock market.

Discretionary consumer purchases are most threatened by the confidence factor, the analysts said. Among these are home improvements, automobiles, consumer electronics and restaurant meals. Luxury goods purchases appear the most jeopardy, since wealthier investors were hurt most directly.

Home builders felt the crunch before the market crash because rising interest rates -- a leading cause of the loss of investor confidence -- had discouraged large numbers of would-be home buyers in recent months.

Kent Colton, chief executive officer of the National Association of Homebuilders, said 31 percent of builders surveyed early last week predicted poor sales in the next six months, compared with only 10 percent in March. Those expecting good to excellent results dropped from 56 percent to 22 percent.

The next several weeks appear crucial to the overall consumer response. If the market stabilizes and Washington asserts reassuring leadership, the impact on consumption would be limited, the analysts said.

"When people are faced with great uncertainty, the usual reaction is not to act -- to wait and see," said Curtin. "That has the negative consequence of withholding sales, but only for a week or 10 days, which is not necessarily overwhelming. The most important thing is whether consumers will sense a firm hand on the economic policy rudder or whether they will believe this is only the tip of the iceberg, unchecked by market forces or government responses."

Allen Sinai, chief economist of Shearson Lehman Bros. Inc., estimated that the plunge in stock prices, if not reversed or offset by some other development, would likely mean a drop in consumer spending of $50 billion to $60 billion by early 1989. Both the decline in wealth and a loss of confidence would be involved.

"As a result, we will lose 1 to 2 percentage points on economic growth through 1988 and into 1989," Sinai predicted.

At the same, Sinai said, businesses will be affected both by the drop in consumer spending and the more direct effect of having a much lower market value for their assets. That could clip another half percentage point from economic growth next year as business investment spending is held down.

If all of the market's decline were quickly reversed, the impact could be far smaller, almost negligible. But if the decline were to resume, it could lead to significant business and personal bankruptcies and a recession, Sinai warned. A recession in the United States could spread quickly around the world, he added.

One positive economic note would be that if consumer spending falls, it could significantly affect purchases of imported goods, which would slightly reduce the nation's large trade deficit.

If the market stays roughly where it was yesterday, Sinai said, the odds of a recession hitting in 1988 are 1 in 3. "If there is some rebound, and if the Fed at the same time eases up, and there is some relief on the trade deficit, I think we could still get through 1988 but with less growth."

On the other hand, if the market's free fall turns out to be transitory, and President Reagan and Congress can get together on ways to reduce the federal budget deficit by about $50 billion, Sinai said, a recession not only could be avoided, "it would be curative. The economy would do better."

Sinai's estimates of the economic impact were close to those of Jerry Jasinowski and George Richards of the National Association of Manufacturers. They said there is about a 35 percent chance of a recession, adding, "The more likely trajectory for the economy is one of slow growth, with the crash subtracting as much as a percentage point from the gross national product over the next three quarters."

That would leave economic growth running at an annual rate of less than 1 percent through the middle of next year, Jasinowski and Richards said.

At the Brookings Institution, George Perry said the market slump would have a significant impact on the economy. "I don't think we should treat this as an event that is confined to the great casino out there. You have taken down such an amount of wealth that it ought to affect spending. It should mean a slower economy.

"I think the authorities are going to have to work hard to put liquidity into the financial markets," Perry said. The added liquidity should mean lower interest rates, which will help the economy, particularly housing, he said.

But Perry cautioned, "I am not sure we are out of the woods. It will be little while before we know how the world financial system has digested this."

Lyle Gramley, chief economist of the Mortgage Bankers Association and a former Federal Reserve governor, said, "I don't think there is much doubt that the decline in stock prices will be a substantial negative for the economy in 1988."

How big a negative will depend upon how seriously consumer and business confidence has been hurt, he said.

Several of the analysts stressed the overriding importance of the role the Federal Reserve must play.

Staff writers Martha Hamilton and Albert B. Crenshaw contributed to this report.