THE GREAT DEPRESSION OF 1990 Why It's Got to Happen -- How to Protect Yourself By Ravi Batra Simon and Schuster. 235 pp. $17.95

As the current economic expansion churns forward into its fifth straight year, all the signs seem to be pointing up. The stock market, personal income, production, consumption -- all are on the upswing. Leading economic indicators forecast continued growth.

But there is something about human nature that can't stand prosperity, a little voice that in times of plenty is forever asking, isn't this too good to last? Isn't it just a matter of time before it all comes crashing down around our ears? And today, as in past boom times, there are plenty of prophets ready to warn us that the end is nigh.

One of the more interesting and provocative of the current crop is Southern Methodist University economics professor Ravi Batra. Not only is he certain that a crash is coming, but he believes he can foretell the date, the extent and the reasons for the catastrophe.

"We can actually pinpoint 1990 as the year of the world's greatest depression," he says. It will be "the worst economic crisis in history," and it is, "given the perverse fiscal policy of the Reagan presidency, inevitable."

Batra, a scholar who has earned a considerable reputation as an expert on trade, is a wave theorist. Cycles in human events come and go in regular and predictable patterns, he believes, and careful analysis of historical data can uncover them.

Examining data on money supply, inflation, and government regulation of the economy, Batra concludes that "in the U.S. economy there has been at least one recession every decade, and a great depression every third or sixth decade." In other words, depressions usually hit every 30 years, but not always. Sometimes we have managed to go 60 years without a crash, but when we have done so "the sixth decade {has} experienced a cumulative effect -- an all-out disaster."

Sixty years from 1930 is, of course, 1990, and since there was no depression in 1960, we are due for a whopper that year.

But why?

At the root of Batra's forecasts is the work of Prabhat Ranjan Sarkar, an Indian thinker who propounded what he called "the law of social cycles." According to this, human society proceeds through a series of cycles, each characterized by the dominance of one of four social groups -- laborers, warriors, intellectuals or "acquisitors."

From the days of the American Revolution and even before, this country has been controlled by this last group, the acquisitors, Batra believes, who are "obsessed with money." Thus American society has been structured to serve the interests of the rich, who as time goes by, accumulate an ever greater share of the nation's total wealth.

But this arrangement is inherently unstable. Excess wealth touches off speculation and other financial excess. "As a person becomes wealthy, his aversion to risk declines. As wealth inequality grows the overall riskiness of investments made by the rich also grows" until so much risk is built into the financial system that it cannot withstand a downturn, and an otherwise ordinary recession spirals downward to disaster.

It was wealth disparity that caused the Great Depression of 1930 and it is wealth disparity that will cause the Great Depression of 1990, Batra argues, citing figures to show that concentration of wealth was the greatest in history in 1929 and is rapidly climbing to similar heights today under President Reagan's tax and fiscal policies.

Only a radical redistribution of wealth can avert the coming disaster. That being unlikely, Batra recommends that individuals prepare themselves by converting most of their assets to cash. Sell your house and any other real estate, cash in your retirement plan, get out of stocks and bonds before the end of 1989.

Banks will fail, so put no more than a third of your cash in a bank account. Put a third in a safe deposit box, he advises, and keep a third at home. He figures that the depression will last seven years -- through 1996 -- and individuals should be prepared to be out of work for at least four of those years. Thus, to make it through at the poverty level, a family of four will need at least $44,000 on hand when the crash comes.

This isn't economics. Batra's recipe is about two parts statistics, two parts Indian mysticism, one part survivalism and one part balderdash. To bring about his crash, Batra must dismiss all the banking and monetary reforms that have been put in place since 1929, and argue that the government would let a nation of debtors go broke rather than "unleash the engines of money growth" in a crisis.

Unlikely as that may seem, however, no one can guarantee that he is wrong. And the historical statistics Batra offers show a disturbingly regular pattern of boom and bust in our economy.

Most striking are the eerie parallels Batra shows between the 1920s and the 1980s. Both decades began with high inflation, high unemployment and high interest rates. There were major tax changes in 1921 and 1981, stock market rises in 1923 and 1983, energy price declines in 1926 and 1986, and other year-by-year similarities.

"Normally, the six-decade cycle is not so precise," he says, "but for the 1920s and the 1980s it is turning out to be as exact as it possibly can be ... If no remedial measures are taken at this time, then 1989 will be like 1929" and we will all be wondering why we didn't listen when he warned us.

The reviewer is national business editor of The Washington Post.