NEW YORK, OCT. 17 -- Whether it signalled the end of a five-year boom or was merely a temporary stumble--and only mystics and psychics dare say they know for certain--the stock market's record-setting dive last week will provide a critical test of worldwide investor confidence and U.S. economic strength, analysts said today.

That test will begin as soon as Monday, when individual investors and big fund managers in Tokyo, London, on Wall Street, and across the U.S. return to the stock market following a welcomed weekend respite.

There are bound to be some early jitters, analysts warned. The stock market's fall last week was harder and deeper than any drop since 1982, when the raging bull market that has stoked U.S. prosperity for the last five years first gathered steam. And while the market is still up 18 percent for the year, a pessimistic mood pervaded the stock market last week.

Rattled by rising interest rates and a perception among investors that the U.S. trade deficit was not declining fast enough, the Dow Jones industrial average plummeted 235 points during the week, climaxing Friday with a record 108.36 point loss. Friday's dive surpassed Wednesday's short-lived record loss of 95.46 points.

Mounting concern among investors during the week degenerated into a frenzied panic during the last hour of trading Friday, as stock prices collapsed amid the heaviest trading in New York Stock Exchange history. Prices rebounded modestly during the final ten minutes, but not enough to relieve the despair expressed by many investors and traders after the market closed.

Hundreds of billions of dollars in value was erased by the market's week-long plunge. According to the Wilshire Associates index of 5000 U.S. stocks, $145 billion in stock value was wiped out just on Friday.

One important question is whether that loss of value will cascade into the U.S. economy during the weeks and months ahead. The nation's rising economy has been fueled since 1982 by robust consumer spending, and that spending has been driven at least in part by prosperity generated in the stock market.

If the market fails to rebound, some economists worry, slower consumer spending could undermine economic growth. Moreover, consumer savings has weakened recently, exacerbating fears that the economy is vulnerable. According to government figures, consumer savings as a percentage of disposable income declined from around 7 percent to near 2 percent during the same five years the stock market has boomed.

As the weekend began, individual investors expressed concern but not panic about the stock market. At Fidelity Investments, the giant Boston-based mutual fund company that reaches millions of individual investors through a vast telephone sales system, spokesman Rab Bertelsen today reported that calls from customers were up about 35 percent over normal levels, but said, "While calls are definitely up, they are not at unprecedented levels."

On Friday, some professional investors on Wall Street worried that individual investors in huge mutual funds such as Fidelity's could trigger a disastrous panic by forcing fund managers to sell large blocks of stocks while the market was in decline. Investors in Fidelity and other mutual funds can demand instant cash redemption of their shares by telephone.

A massive demand for cash redemptions might force portfolio managers controlling billions of dollars of stock to sell shares into a collapsing market in order to raise the cash necessary to redeem shares owned by individual investors. Such selling might push the stock market into a downward spiral.

Bertelsen discounted the likelihood of such a scenario. He said Fidelity stock fund managers had lines of credit available from banks that could help pay off redeeming customers without forcing stock sales into a down market. "At this point, the system is working," he said, but added, "A great deal depends on what happens next week, obviously."

The potential economic fallout from a down market is not limited to its effect on individual investors. Though there is little agreement on the issue, some leading Wall Street dealmakers have expressed concern that American corporations have far too much debt on their balance sheets as a result of increasing takeover activity.

A declining stock market, these observes warn, could render prohibitively expensive those takeover deals that depended on heavy borrowing at the height of the market boom, possibly leading to dramatic losses or corporate bond defaults.

Such gloomy scenario-spinning was commonplace on Wall Street by day's end Friday, but the fears could quickly subside if the stock market bounces back strongly this week. And that will depend not only on the reactions of individual investors and fund managers in the U.S., but on the attitude of foreign investors, particularly Japanese, who have been pouring money into the U.S. stock market in recent years.

Japanese investors bought $3.5 billion of U.S. stocks during the first three months of 1987, according to government statistics, and foreign investors have been buying stocks at an annual rate of $39 billion so far this year. At the end of 1986, they held $167 billion in U.S. stocks.

Wall Street will be watching closely this week to see whether overseas investors beat a fast retreat from the stock market, and also whether stock markets in Tokyo and London show ill effects from the Dow's swoon.

The Tokyo stock market is considered especially vulnerable by many U.S. analysts. Leading Japanese stocks have been selling recently for as much as 70 times earnings, far above the average U.S. range of 15 to 20 times earnings. The relative cheapness of U.S. stocks in comparison with Japanese stocks has attracted billions of dollars of Japanese capital during the U.S. market boom.

Mesahiko Goto, an analyst with New Japan Securities International, noted that both the U.S. and Tokyo stock markets have been driven upwards by the growing Japanese trade surplus. He said that inflated stock and real estate prices in Japan--as well as the strength of the U.S. bull market--are due partly to the fact that many Japanese investors feel they have no place else to put their cash.

"The world is so small, certainly a fall in the New York markets should bring some cautious psychology to the {Tokyo} market," Goto said today. "We may see some selling next week. But I think the downside is quite limited because of the situation of excess {cash} in Japan."

Goto said that Japanese investors, like U.S. investors, will be influenced by rising U.S. interest rates that make bonds a relatively attractive investment, compared with stocks. But he said that he would be surprised if Japanese investors made a dramatic shift over the next few months away from the U.S. stock market.

"As the {stock} market goes down, it will be giving more opportunities for them to come in. They are more long-term oriented. There may be even more investment from the Japanese in the U.S. stock market" than before the Dow's dive, he said.

Long-term confidence in the U.S. stock market, of course, depends in large part on the performance of the U.S. economy. The present outlook of moderate inflation and rising interest rates is sending mixed signals to investors, both here and overseas, analysts said.

Interest rates remain the single most important factor in the short-term performance of the stock market, analysts said. Steve Einhorn, partner and co-chairman of investment policy at Goldman, Sachs & Co., a major Wall Street investment firm, said Friday that "one of the most important messages of the last couple of weeks is that the stock market has found its threshold of pain in terms of long-term bond yields, and that threshold of pain is 10 percent."

Another lesson from the Dow's recent performance, some investors and analysts said, is that the stock market's climb this year has been uneven. For one thing, stocks soared while the bond market headed steadily in the opposite direction.

Even within the stock market, the boom has not been uniform recently. While the Dow average of 30 leading industrial stocks soared during the first nine months of 1987, broader measures of market performance, such as the New York Stock Exchange's advance/decline line, which tracks the ratio of winners to losers on the entire exchange, remained flat.

And whereas when the Dow crossed 1000 points in 1982, more than 1000 stocks achieved individual record levels, in 1987--even when the Dow smashed the 2500 barrier--less than half as many stocks posted all-time highs, according to statistics compiled by Butcher & Singer Inc.

Those trends suggest to some investors that the rise in the Dow has been fueled more by short-term, speculative investment and what one major portfolio manager Friday termed "Wall Street salesmanship" of selected major stocks than by any broad market strength.

If its dive last week serves to bring the Dow closer in line with general stock market performance and the bond market, some market observers said, then the correction may be temporary and even beneficial.

Either way, it is certain to make a lasting impression on Wall Street. Many of the young traders, investors, and dealmakers who have profited enormously from Wall Street's boom and who have come to symbolize its fast-paced culture have never worked in a down market, several senior Wall Street investors noted Friday.

If last week's dizzying stock market fall continues Monday, the newcomers will receive a fast, potentially painful, but no doubt enduring lesson.