Come nightfall, the sound heard in every corner of this hardworking nation is the clink of glasses and happy shouts of "Kampai," - cheers. The Japanese national thirst is growing - too rapidly for some doctors who worry that people are drifting from workaholism to alcoholism.

Problem drinkers number 2 million, or almost 6 per cent of the adult population according to a recent survey of drinking habits. "Alcoholism is increasing in Japan," said Dr. Hiroaki Kono, director of the National Institute of Alcoholism." We were astonished at the size of the problem."

The causes of the excess merrymaking are thought to lie in the stresses of profound social changes and a traditional Japanese reliance on alcohol as the universal icebreaker. Post-industrial afluence has given the Japanese working man more leisure time to drink and more money to enjoy it. Additionally, the survey found that while Japanese women are far from liberated, they are joining their menfolk at the bar. More than 52 per cent of the women polled take an occasional drink - up from 18 per cent only eight years ago.

Clearly pinpointed by the study were the dangers of the semi-obligatory drinking required of Japanese salarymen - white-collar workers - to settle differences and cement personal relationships. Sixty per cent of the problem drinkers turned out to be businessmen who claimed the mizuwaris - whisky and water - they sank with clients were an essential extension of office hours.

Money makes the world go round, but in Japan where emotions are veiled for the sake of harmoney, alcohol greases the wheels. After sublimating tension and frustration all day, people in every walks of life turn to alcohol for socially licensed release. There is no taboo against getting drunk - indeed the Japanese suspect that a collegue who holds back is afraid of the innermost feelings which might surface.

"Alcohol here plays the role of psychiatry in the West," said a foreign diplomat, "I think the country would explode without it. Instead of analysis they get rid of their inhibitions with a few drinks. You can say and do anything - tell the boss off and get away with it."

In the far northern city of Sapporo a company president explained some disagreeable facts of commercial life to a young employee. After a few drinks the mood got mellower. The two men left arms on each other's shoulders, drunk and smiling.

In Nagoya, the city detectives drink late at night in a tiny private bar. They talk crime business and complain about their bosses. Yet they make the morning shift on time - alcohol absenteeism and Monday morning hangovers T

The scenes are repeated in the mizu-shobai - meaning "water business" entertainment districts of every town and city. Day laborers drink a cheap white lightning. High-paid executives gather in the gloom of cabarets to nurse whiskies and dandle hostesses. "They are very tired by business and its our duty to help," said the virtuous manager of $40 a-head club.

Every year the national tax agency announces consumption of alcoholic haverages with a picturesque vision of it all being poured into the nation's tallest skyscraper. In 1970 the Japanese drank enough to fill it to the brim 10 times. Last year they drank 12 buildings full. Cirrhosis of the liver - a disease frequently related to alcoholism - is increasing.

Expense account businessmen who say that 35 per cent of their visits to bars are necessary to smooth out inter-personal relations, dropped $670 million on entertaining in 1976. Tokyo police report that more drunks than ever needed a night's lodging in the drunk tank - the Japanese call them "torabako" meaning tiger box - last year. Like their counterparts in other nations, the Japanese see a definite correlation between alcohol and the incidence of violent crime and suicide. Af all murders, approximately 37 per cent are committed under the influence of alcohol.

Younger office workers quaff tankards of beer in rooftop beer gardens where go-go dancers mechanically gyrate to pounding rock bands. The German restaurants are crammed with young Japanese gulping ale from boot-shaped glasses and singing Lili Marlene to neo-tyrolean bands. Thirsty pedestrians can always get a cold can from the streetside beer dispensing machines, or join the tipplers at a cheap food stall.

All over Japan the traditional rice wine - sake - is on the run as whisky consumption goes up 12 per cen annually. In a favorite sushi shop where whisky is the drink of choice, I once saw a young couple get steadily plastered. Eventually the young man half-carried, half-dragged his insensible girl friend away while the other customers unconcernedly sipped on.

In ancient times the revelry was limited to shinto festivals. The carousing goes on year round now without constraints. The countless bars in the narrow lanes of Ginza open at 5 p.m. and daytime decorum vanishes as the offices close. By 10 p.m. sobriety is a rare phenomena. Good-natured hostesses load the tottering clientele into taxis and limousines while other well-laden drinkers sway boisterously off to the subways.

Indulgent public attitudes to excessive drinking and the social mechanisms which actively encourage it, are deeply disturbing to Dr. Kono. Adult consumption is far below American levels, but in the teen-age drinking binges here which occasionally result in alcohol poisoning deaths, he sees a new menace: "This is very worrying because we have no Christian taboo against drinking Japan. Twenty per cent of our high school students are drinking once a week . . . if it catches fire it would be like matches on oil."

Without positively asserting a casual relationship, Kono says drinking is increasing fastest in the big cities and remote rural areas where social change is most disruptive. He saves his severest criticism for the blurring of work and private life which involves near compulsory drinking. "Even in a hospital where alcoholics are treated," he complains, "the doctors are expected to drink together to show human communication."

Hospital treatment is backward and the facilities inadequate, Kono declares. After gathering $3.5 billion in alcohol taxes last year, the Japanese government budgeted just $19,000 for alcoholism research, according to Kono.