THERE, AT LAST, is a simple solution to an exceedingly complex problem. To restore U.S. industrial competitiveness and create jobs, Americans should flock to their banks or their brokers and trade in their dollars for Japanese yen.

Such a nationally organized run on the yen could have all sorts of benefits. Almost all the experts agree that today's yen is a bargain that is bound someday to be worth considerably more than the 235 per dollar it now fetches, so Americans who join the bandwagon early could reap profits later.

More important, a yen--buying spree could drive up its value to the point where Japanese companies could no longer undersell American firms in the world marketplace simply because the currency values of the two nations were badly out of whack.

Yen populism, as one might call it, has a trace of plausibility because the statesmen meeting this weekend at Williamsburg seem unable to solve the problem of international exchange rates through traditional diplomacy. All the participants at Williamsburg know that the continuing misalignment of the dollar and the yen is a symbol of disarray in the international trading system.

If our leaders cannot act, maybe American companies, workers and union pension funds should consider taking matters into their own hands.

The connection between trade and foreign exchange rates is straightforward. Most foreign trade is conducted in dollars. When the yen goes down in value it means a Japanese car company can charge American customers fewer dollars and still collect as many yen as before when it converts the dollars back into its own currency.

This is what has been happening to U.S. industry.

Consider, for example, the tribulations of Caterpillar, the largest U.S. manufacturer of earth moving equipment. In the first part of 1982, when the yen was trading at between 230 and 260 to the dollar, Caterpillar steadily lost sales to its leading competitor, Japan's Komatsu. Caterpillar's overseas sales fell by 14 percent in the first half of the year, while Komatsu's rose by almost 50 percent. Caterpillar won't become competitive again until the yen gets stronger.

It is the same in cars and computer chips. If the yen is undervalued by 20 percent, as many experts think it is, then Japanese automakers can keep the dollar price of their cars about $1,500 less than it would be in a fairer world -- or they can keep prices higher and reap a windfall.

These distortions have little to do with the relative efficiency of Japanese and U.S. industry. Instead they are produced by an international financial system that works better for speculators and financial managers than for the producers of goods.

There was a time when the value of a currency was believed to have some connection to the underlying health of an economy. Those days are now over.

The United States, with 4 percent inflation and a 1983 trade deficit that some think could reach $50 billion, now has the "strongest" currency in the world. The Japanese yen, currency of a nation with almost no inflation and a trade surplus that could hit $50 billion this year, is among the weakest.

Why? Because currency valuations today have little to do with fundamentals of that kind. Instead the yen and the dollar are muscled around by massive movements of money flowing back and forth across borders, sometimes for no more than a few hours, in search of the highest available interest rates. Not surprisingly, given the continuing high interest rates in this country, companies and individuals all over the world (especially Japan) have been converting their funds into dollars, to buy U.S. bonds, certificates of deposit or other instruments. This is what makes the U.S. currency "strong."

According to economist C. Fred Bergsten, director of the Institute for International Economics, capital left Japan at the rate of about $1 billion a month in 1981 and the first part of 1982, and $2 to $3 billion a month during the last year.

It is tempting to blame the banks and the multinational companies for this state of affairs. After all, it is the banks and the companies, primarily, which are moving the money and causing the pain.

"A few of them together are big and powerful enough to effect what a currency does on any particular day. But that power should not be confused with the ability to sustain artificial exchange rates over a long period of time. "Not even Walter Wriston (chairman of Citibank) is powerful enough to put the bear squeeze on a currency all by himself," as a Wall Street banker put it.

The real culprits are the governments -- especially the U.S. government. The misalignment of the yen and the dollar that has wrought such havoc on U.S. industry is the second part of a monetary double whammy inflicted on the economy by the Reagan administration and the Federal Reserve. The combination of the Fed's "tight money" policy -- which amounted to restricting the number of dollars in circulation, and which the Reagan administration encouraged -- and the huge deficits proposed by the administration and voted by Congress produced high interest rates. High interest caused a drastic turndown in the American economy. At the same time, record interest rates attracted an international stampede of funds into dollars and dollar instruments, thus inflating the relative value of the dollar.

When the postwar system of fixed exchange rates was abandoned in 1973, the new system of "floating" rates was supposed to provide a guide to economic policy makers. When a country's currency got too badly out of line, it was assumed, that would be the signal to change the mix of economic, fiscal and monetary policies in that country. It hasn't worked that way.

In the last five years, Tokyo and Washington have had plenty of signals. The yen has been on a roller coaster ride, going from a top value of 176 to the dollar in October 1978, to a low value of 278 to the dollar in November 1982. (It closed at 235 Friday). Yet neither government has taken decisive action to stabilize these movements at a level that would bring the Japanese trade surplus into line.

The Reagan administration, preoccupied with controlling inflation, has allowed interest rates to remain high and has used protectionist style measures, such as the "voluntary" quota on Japanese auto imports, to stem the incoming tide of Japanese products. Economist Bergsten argues that the policy has been shortsighted and self-defeating. The voluntary quotas, he contends, have removed any incentives for the Japanese automakers to cut their prices since the deal cut between the two governments prohibits them from taking a larger share of the U.S. car market than they already have.

Bergsten says that the Japanese automakers have taken advantage of the fixed ceilings on the volume of their sales to raise prices here substantially and to sell higher priced luxury models that earn more profits. "As a result of the interaction of these two phenomena, the profits of these firms have skyrocketed and positioned them to be even more formidable competitors in the future," he maintains.

If the U.S. government bears primary responsibility for this state of affairs, the Japanese government also has been considerably less helpful than its official rhetoric might suggest.

Lawrence Krause of the Brookings Institution, lays 70 percent of the blame on the U.S. government, and 30 percent on Japan. "The Japanese say the problem isn't the weak yen but the strong dollar. They're partially right. But they are also responsible."

Japanese officials advertise the decline in their foreign exchange reserves as evidence that they have been intervening in the markets to prop up the yen whenever it shows signs of weakening. They stress that their trade surplus is misleading. Japan, they note, pays out billions each year for services, which do not show up in those figures.

But Krause cites several examples on the other side of the ledger.

After reaching its lowest value of 278 to the dollar last November, the yen finally began to strengthen as Japanese became convinced that the decline in U.S. interest rates was more than a temporary development, and speculators began to contemplate a much larger Japanese trade surplus in 1983. But after the yen had gained some 20 percent in value, officials of the Bank of Japan quietly began talking about a cut in the Japanese discount rate, which had held steady at 51/2 per cent since December 1981.

Such a cut would help maintain the spread between U.S. and Japanese interest rates and make the dollar a continued good buy. According to Krause, these suggestions put the brakes on the yen's ascent, stalling it out at 235 to the dollar, where it has been ever since. (The Japanese discount rate remains at 51/2 percent.)

Now Tokyo is "awash with money," according to Krause. And as long as the banks have plenty of money to lend, the enormous pressures for Japanese interest rates to go lower are going to continue.

Another unhelpful step, in Krause's view, was the Bank of Japan's removal of restrictions on the purchase of some foreign bonds by Japanese, as of Jan. 1. That kept money flowing out of yen and into U.S. securities.

U.S. financial experts say there is plenty the Japanese government could do to knock another 20 percent off the value of the yen. Rimmer De Vries, senior vice president of Morgan Guaranty Trust Co., points out that the Japanese government could delay reducing its budget deficit and increase government spending to stimulate Japan's stagnating economy. The resulting government borrowing would prop up Japanese interest rates by soaking up some of the money that is inundating Tokyo's financial community.

Plenty of Japanese would like to see a currency realignment. These include manufacturers that pay out expensive dollars for oil and raw materials, and sophisticated Japanese Trilateralists who are fearful of a worldwide backlash against the tidal wave of Japanese exports. But they haven't been strong enough to sway their government.

Strengthening the yen would not end U.S. trade frictions with Japan. The special U.S. problems with Japan go deeper. A dollar that is considered overvalued in relation to the French franc and German mark hasn't prevented the United States from running large trade surpluses with those European countries. So factors other than exchange rates must be at work in the U.S.--Japan trade wars. If and when the yen strengthens, Japanese companies may opt to maintain their exporting drive and swallow the losses while they keep gaining markets.

But a realignment is needed to prevent more serious political tensions between the two countries. The 1982 U.S. trade deficit with Japan was $16.7 billion -- in the middle of the worst recession in years. If the U.S. economy recovers, the deficit could go much higher in 1983 as freer-spending Americans buy even more Japanese goods.

That kind of surplus is supposed to be self- correcting. As Japanese companies convert the dollars they earn here back into yen to do business at home, the yen should strengthen, helping U.S. exporters.

But in the continued absence of concerted action by Tokyo and Washington, other forces (such as a new round of higher U.S. interest rates) could prevent the correction and keep the dollar inflated.

That is why, in the face of government inaction, yen populism may not be all that far-fetched. If converting the family savings into yen would help force the price of the Japanese currency up to where American industry can survive, it might just be worth a case of speculator's nerves.

If giant multinational companies who have been losing out to Japan's industry don't have theeheart for this kind of plunge, maybe the man on the street will have to lead the way.