Herbert Hayde, president of the American Chamber of Commerce in Japan, keeps track by what his standard haircut and manicure at a Tokyo hotel would cost if he paid in dollars. Seven months ago it was about $42. Two weeks ago it was $61. By last week, it had climbed again, to about $63.

Just about every foreigner living in Japan these days has a gauge like this to bring to personal terms the spectacular plunge of the value of the U.S. dollar that began in September and continues with no end in sight.

Even with the dollar strong -- as it was through most of 1985 -- Japan is a country of legendary expense, especially in food and housing. Now, in terms of dollars, everything costs 50 percent more than it did in September.

Many Americans living here praise the realignment as a crucial step toward righting Japan's trade surplus with the United States, which totaled about $50 billion last year. The new exchange rates tend to make Japanese products more expensive to foreign buyers.

But at home, the turnaround in the dollar's fortunes means family budgets rendered absurd, vacations canceled and once-routine pleasures of life in Japan turned into extravagances.

It has brought out the gambler's instinct in everyone. Has the dollar bottomed out? Should I convert a chunk of dollars now or gamble on the rate moving back up? Surely the dollar can't fall any further. But, then, no one ever expected it to come down this far.

Often luck is what counts. One American resident here had the good fortune to decide to buy a large quantity of Japanese stock just before the dollar's crash and has been meeting living expenses ever since by selling it off bit by bit.

The dollar rose to about 260 yen in early 1985. It softened to 240 by September and then began a tailspin after finance officials from the United States, Japan, Britain, France and West Germany, met in New York and launched a program of coordinated intervention to bring its value down. The dollar now is worth about 168, an improvement over last week, when it fell to 160, its lowest point ever.

There are still a few bargains to be had in Japan. A three-minute call on a public phone costs just 6 cents, even at the new exchange rates. A ride on the clean and reliable subways of Tokyo goes for 75 cents.

But a stroll through a grocery store puts things in better perspective. There recently, a single stick of celery was offered for $1.25, a head of lettuce for $1.56, a large tomato for $1.56 and a smaller one for $1.38.

A two-bedroom apartment with a 20-foot-square garden in Tokyo's Shinagawa ward was being offered this week for almost $6,000 a month. A three-bedroom, two-bath apartment in the Hiroo district, admittedly a prime location, was going for $12,500.

Foreigners never stop talking of beating all of this. Best protected are expatriate employes of large foreign banks and corporations. Especially envied are those of International Business Machines Corp. They get a cost-of-living allowance plus rights to convert a portion of their regular salary from dollars into yen at a fixed rate. Their housing is heavily subsidized, too.

Other foreign companies refuse to offer fixed exchange rates but give help with housing and pay cost-of-living allowances, which float up and down as currency values change and are supposed to cover any losses.

U.S. military and embassy people, meanwhile, get heavy protection through free housing, cost-of-living allowances and access to commissaries and post exchanges. Their nonofficial dinner guests are astonished at the size of the steaks served on their plates.

Worst off are those people living on fixed-dollar incomes, such as academics here on research grants. One American historian found that, when he first got here, he could just about make ends meet on his monthly stipend of $1,085. Now, he laments, "I've borrowed $2,500 to make it to the end of my stay here -- I borrowed it from my mother back in California."

With that and about $280 a month from illicit English teaching and translation, he is getting by. "It's an abuse in a way, but it's kind of self-defense. I don't want to just wither on the vine," he said.

But some foreigners, like Stephen Burke and Cindy Murphy, an American married couple employed by Sony Corp., are doing well by it all, at least on paper. They are paid in yen. When the dollar started falling, Japanese office mates began what became a familiar joke in the morning. "They would say, you got a raise. The very first time this happened, we were ecstatic," said Burke. " . . . Then they would smile and say, 'En daka' [strong yen]."

Between them they were making the equivalent of about $35,000 when they began at Sony last year. Now their salaries are worth together close to $50,000. "But we live in Tokyo and pay Tokyo prices," Burke said. "In that sense, it hasn't increased or decreased our buying power at all."

Word has spread abroad, meanwhile, and tourists are starting to think twice. The staff of Tokyo's Imperial Hotel has noticed fewer orders for room service. At Sakura-ya discount camera shop, many foreign customers are not coming at all for its duty-free wares. "During the best times, sometimes we got 300 or 400 buyers per day. They would come as a group. Now it's maximum four or five persons per day," said Etsuji Amagi, a sales manager there.