When I arrived in Tokyo one morning a few weeks ago, a friend with good connections there did me the favor of getting me a room in one of the city's better hotels.

Some favor.

The room cost $110 a night - not including breakfast coffee, which ran to $3 a cup.

According to the statisticians, Tokyo is the most expensive city on earth. Prices are especially astronomical for Americans, however, since the dollar has plunged in relation to the Japanese yen by 40 percent in the past couple of years.

But our plight in Tokyo is only a grotesque exabberation of the situation we face, to some degree or another, nearly everywhere in the world - and for the same reason.

Though the dollar is still the accepted currency for international transactions, it has faded into a pale green shadow of its former self, and it may be only a matter of time before it becomes prohibitive for an American to go abroad.

If anything is contributing to U.S. isolation, in fact, it is the dwindling value of the dollar, which is making an American presence overseas increasingly difficult.

Ironically, there is a vicious cycle in this state of affairs.

The fall in the dollar is due in large measure to the whopping U.S. trade deficit, mainly the reflection of rising oil imports. The deficit, which was $26.5 billion in 1977, may escalate to $34 billion this year.

But the American companies whose activities are vital to U.S. trade are finding it harder and harder to function in foreign countries because, as a result of the dollar's drop, their expenses are so high.

Maintaining an American company representative in some European capitals, for example, can cost twice his salary in office and travel expenses, housing allowances, educational benefits for his children and the rest.

In many places, rents are $1,000 or even $2,000 a month, with companies picking up the tab. Americans in some foreign countries must pay local income taxes in addition to their U.S. tax, and here again the company makes up the difference.

The Wall Street Journal, which monitors such things, reported recently that firms like Warner-Lambert, General Data and the Marine Midland Bank are closing some of their European offices or retreating to London, a somewhat cheaper place to do business.

American newspapers, magazines and television networks also have been shutting down their foreign bureaus because of high costs. Editors tell me that keeping a correspondent overseas can run to $100,000, sometimes even more, depending on the area.

One of the more paradoxical sights abroad these days is the spectacle of U.S. soldiers in West Germany. They are a far cry from the Gls who marched across Europe during World War II, handing out chewing gum, candy bars and cigarettes to the people they had liberated or conquered.

Today the Gls stationed in West Germany are financial basket cases. The 20,000 or so who have their families with them often have to turn to relief agencies to make ends meet. Even the extra stipends furnished by the Defense Department - which will cost U.S. taxpayers $200 million this year - are not enough.

All this means, quite plainly, that there is not much incentive for Americans, either civilians or soldiers, to serve overseas. The exceptions may be engineers and construction workers in places like Saudi Arabia who are on get-rich-quick assignments.

Traveling abroad frequently as I do, I find it difficult to avoid recalling the way it was when, in the years after World War II, I lived in Paris as a student.

On a visit there not long ago, I made a simple calculation and discovered that I was paying the same for one night in a hotel now that I paid for a year in a Latin Quarter hotel a generation ago. My standards have changed, of course - but not that much.

In those days, too, it was possible to exist fairly comfortably in Paris on the GI Bill, which paid $75 a month. My daughter, who currently has a summer job in Paris, has trouble getting by on twice that amount a week - living frugally.

This situation, I think, also is going to work against us over the long run. For as the Unites States becomes increasingly reliant on the rest of the world, fewer and fewer young Americans are going to be able to spend the time abroad necessary to develop an "international vocation."

In the years ahead, therefore, we could encounter a shortage of Americans familiar with foreign languages and cultures, and that is bound to impair our global position, particularly in the economic sphere.

This all argues for dynamic U.S. measures to strengthen the dollar - not only through an energy policy that reduces our dependence on imported oil but also industrial innovation to produce American manufactured good for sale overseas. Outside of aircraft and automobiles, we export very little in the way of manufactured products.

The alternative for Americans who want to travel abroad is to make lots of foreign friends who will provide food and lodging, so we can politely decline the favor of $100-a-day hotel rooms and $3 cups of coffee.