One of today's great cottage industries is making American- Japanese comparisons. Here's one that almost everyone has probably heard: Japan saves almost twice as much as the United States. We are said to be in deep trouble. Japan will out-invest us and achieve higher living standards.

Well, maybe. But for now, the high savings rate is having the opposite effect: It's a drag on Japan's economy -- and on the rest of the world's, too.

If you're expecting a tirade against Japan, stop reading now. I offer Japan's high savings rate only to explain why economic summit meetings, like last week's in Bonn, can't accomplish much. We live in an economically interdependent world, but the most serious economic problems are deeply embedded in our separate societies, making global economic coordination virtually impossible.

Japan's high savings rate is only one of many examples. The United States' budget deficits and tax policies prop up American and worldwide interest rates, hampering growth abroad. In Europe, high wages, excessive regulation and generous welfare benefits have made economies rigid and less capable of growing, which in turn increases America's trade deficits. And, in many developing countries, triple-digit inflation retards economic growth and makes overseas debt more burdensome.

But none of these problems submits easily to international negotiation. The paradox of economic interdependence is this: Most countries are affected by economic conditions in other countries; but the economic strengths and weaknesses of any country -- which affect everyone else -- are peculiarly domestic. They reflect nations' histories, politics and values; they aren't easily changed from inside, let alone outside. The global economy is hostage to these national inconsistencies.

Consider Japan's savings rate. It represents both economic strength and weakness. For decades, it provided inexpensive investment funds to business that propelled Japan's high economic growth. But it also reflects biases against consumer spending that now hurt Japan's economic growth and living standards. Housing is expensive. Consumer loans are scarce. And the high savings rate depresses the yen's exchange rate, bloating Japan's trade surplus and intensifying protectionist pressures elsewhere.

In 1984, Japanese savings equaled about 27.5 percent of output compared with 18.5 percent in the United States. Japan's domestic investment and huge government deficit absorbed about 90 percent of this, but substantial savings remained to be invested abroad. Japanese insurance companies, banks and companies sold yen and bought foreign exchange -- mostly dollars -- to invest overseas. In 1984, Japanese long-term foreign investment totaled about $50 billion, according to Salomon Brothers Inc. About 70 percent was in dollar securities, mostly bonds.

Notice the implications. The excess of Japanese domestic savings over domestic investment drains potential spending from Japan; the sale of yen for dollars depresses the yen's value, making Japanese exports more competitive and imports into Japan more expensive. Slow domestic growth and a low yen virtually guarantee a huge trade surplus. Meanwhile, housing investment and consumer spending in Japan are lackluster. Everyone would be better off if Japan saved a bit less and spent a bit more.

I'm skeptical this will happen soon. As economist Gary Saxonhouse of the University of Michigan points out, the high Japanese savings rate reflects the peculiarities of Japanese real estate taxes, banking system and general tax policy. According to Saxonhouse, Japanese consumers (who supply two-thirds of national savings) save for three major purposes: to buy a house, to send children to college and to provide for retirement. Because the costs of the first two are extremely high, so is savings.

Saxonhouse says the main reasons are:

* Low real estate taxes on farmland. Low taxes keep land in farming, which aggravates the shortage of real estate for housing. This pushes housing prices up.

* Scarce and expensive consumer loans. The typical home down payment is 35 to 50 percent of cost. College loans are almost nonexistent. Aside from mortgages, consumer loans amount to only 1 percent of total bank loans. And Japanese consumers can't deduct interest payments on loans from their taxes, while most income from savings deposits is tax-exempt.

* Low interest rates on consumer deposits. Until recently, most consumer savings flowed into accounts with fixed interest rates that barely matched inflation. Although some higher-yielding deposits are now available, this is still true. It means that Japanese consumers subsidize business investment and -- to meet their own personal goals -- must save more.

The Japanese savings rate is a parable for the problems of an interdependent world. The peculiarities of national economies often interact in mutually harmful ways. One reason Japanese savings flow to the United States is that interest rates are higher here -- a reflection of our tax and budget policies. The deficits and tax policies (which make interest payments on loans tax deductible) have a pro-consumption bias; Japan's have a pro-savings bias.

But these disturbances can't be managed easily, because they are the unintended side effects of domestic policies. We no more want the Japanese tampering with our policies than they want us tampering with theirs. In each country, existing policies have their beneficiaries and defenders. Change is possible, but at best occurs slowly and haphazardly. Even then, the legacy of ingrained habits lingers. Changing Japanese policies might not produce a quick response in Japanese saving, Saxonhouse says.

When the economic summits started in 1975, they were a reaction to the recession induced by high oil prices and inflation; the main purpose was to prevent trade protectionism. Later, in 1978, there was an unsuccessful stab at coordinating economic policies. But, as the summits have continued, they have become more show and less substance: symbols of the impasse between domestic politics and global economics.