There are fewer than five million Finns in Finland, but this clean little country has nearly a million saunas--those perspiration-inducing baths that employ heat and occasional bursts of steam to produce air temperatures usually found around the open hearths of steel mills. The Finns are so fond of saunas that they patronize them everywhere--in the backyards of their homes, in apartment buildings and dormitories, in factories and hotels, and in thousands of summer villas alongside icy lakes.

The sauna is a way of life, not just a sweat bath. Married couples invite friends over for Saturday night saunas, conversation and elaborate postsauna refreshment. Family members find togetherness and relaxation in taking a sauna at the same time. Finnish businessmen, says one of the many books on the subject, delight in taking "their adversaries to the sauna. Hostility melts in the steam as . . . stubborn minds begin to accept compromise. Rank and protocol are shed in the dressing room with one's clothes, and it is hard to maintain pompous dignity in a birthday suit."

I shed my clothes, rank and protocol recently at the insistence of a Finnish friend, Erkki Palonkorpi, and joined him in the sauna of Helsinki's Palace Hotel, an elegant bath-suite with a private porch overlooking the passing ships in South Harbor. Naked, I gasped my way into an inner chamber where a heap of hot stones in a stove radiated scorching heat. I took shelter on a wooden platform covered with a towel but quickly jumped up as the place where I sit felt searing heat. My friend poured a ladle of water over the bench and I was able, gingerly, to hunch down again.

It was hot! A large wall thermometer showed the air temperature to be 212 degrees, enough to hard-boil an egg just by letting it remain on the bench alongside me. The 212 degrees is an average sauna temperature; some hearty Finns heat their chambers up to 266 degrees !

My mentor, Erkki, is the Finnish Tourist Board's representative in Amsterdam and, like most Finns, is a sauna addict. He is building his own sauna in his backyard in Holland, and, since it is not quite ready, he looks forward to coming back home to Helsinki. Last week. Erkki confided with pleasure, he had to take eight saunas in the process of entertaining visiting travel agents.

"I've had thousands of saunas," Erkki told me, "but I never get enough. I had my first one when I was nine months old. The average Finn takes one or two a week; I could take two a day."

The sauna dates back thousands of years in time, Erkki lectured, beads of sweat forming on his nose and forehead. It originated in the Central Asian reaches where the Finnish tribesmen are said to have lived. At first, the sauna was just a dugout in the ground. Later, it became more elaborate and, like the kitchen, a center of the Finnish household. "Well into this century," Erkki said, "babies were customarily delivered by midwives in the sauna--the cleanest place in the house."

We both put our heads down in our hands, resting our elbows on our knees. The sweat was beginning to drip in earnest now, pitter-pattering on the wooden duckboards. Suddenly, Erkki stood up, dipped hot water from a basin, and scattered it cautiously over the fiery stones. The resulting steam took my breath away, and the sweat poured out even faster as the thick cloud surged over the platform. Unable to inhale, I held my breath. After a minute, Erkki took pity on me. "Let's get a whiff of air," he suggested.

A moment later, we were standing naked, I somewhat shyly, on the open porch overlooking the harbor, inhaling deeply of the cool air. The people in the street below appeared unmindful of this spectacle. Erkki handed me an icy beer and we enjoyed the magnificent harbor view. In case of hunger, a sauna sausage was waiting, circular like a bicycle tire, but tricycle size, greasy and salty. Back to the sauna we went, then out again. Another beer. Back in. Then Erkki reminded me of the sauna books he had loaned me. One of them warned: "An aspect of the public or hotel sauna which a foreigner may find alarming if not warned in advance is the appearance on the scene of a large and benevolent 'kylvettaja' or washerwoman." Another of the books added: "These strong, friendly female attendants are skilled workers, and when they scrub, they scrub thoroughly. between the toes and behind the ears as well. There is nothing to feel embarrassed about. They have seen thousands of naked men and consider them no stranger than clothed men."

Sure enough, the "strong, friendly female" attendant opened the door. I cringed. Her name was Lydia Hurskainen, and she had been a bath attendant in Helsinki for over 20 years. Sure enough, our not wearing clothes didn't disturb her, for she picked up a bundle of birch leaves and enthusiastically began to beat my back and arms with an even rhythm, making them even redder than they were from the broiling. Putting aside a guilty thought about Dr. von Krafft-Ebing's comments on sadomasochism, I decided I liked the beating, especially when Miss Hurskainen finished.

But suddenly I was three years old and helpless as Miss Hurskainen put aside the switch for a very rough, soapy washcloth that she used, as advertised, to "scrub thoroughly, between the toes and behind the ears as well." Then, after flinging a pan or two of chilled water over me, Miss HurslKainen was content to let me take a shower.

Afterward, modestly wrapped in a robe and nursing my fourth beer, I had a chance to interview her. In America, I told her, many people regard a bathhouse as a place of sin, reserved for moral degenerates. Miss Hurskainen was shocked. "Never, never in my 20 years in bathhouses," she assured me, "have I seen a single case of sin. You have to remember that to us Finns, the sauna is a holy place."

Erkki would not let me get away from his country with just a hotel sauna. The next day found us in North Karelia, near Koli, a wildly beautiful part of Finland with lakes and forests, just a few miles from the Soviet Union. A farmernamed Kukkonen had kindly invited us to use the sauna outside his house. Mr. Kukkonen was saunarich. For everyday use, he and his wife, who teaches the first and second grades, have a sauna inside their house. But Wednesday and Saturday between 7 and 8 p.m., the outdoor sauna is fired up. Mr. Kukkonen is currently working on a third sauna, perhaps for a family reunion.

Mrs. Kukkonen has a washing machine, so unlike other farmers' wives, she doesn't use the sauna as a laundry room. However, she follows the old custom of saving all of her soiled sheets, tablecloths and napkins from December to May, while the lake in their backyard is still frozen. Then she washes the linens at one time over the sauna stove and rinses them in the thawed lake.

The best feature of the Kukkonen sauna was the 50-foot-high birch tree that stood outside its door. Holding a glass of unsweetened cranberry juice in our hands, we cooled off in the birch's shade, looking out over the tranquil lake and forest. Afterward, there was an inevitable post sauna repast: coffee, pastries and ice cream.

With traditional Finnish courtesy, my sauna mentor had allowed for my tender skin during those two saunas, limiting our stay in the hot rooms. But my downfall came at a log-cabin smoke sauna not far from the Kukkonens. Smoke saunas are still traditional in rural areas. All the smoke from the burning birchwood stays inside the sauna while it heats and is vented at the last moment, just before the bathers enter, through a plug in the wall. The smoke is so thick that such a sauna does in fact double as a smokehouse. The heat produced is intense. The first time Erkki threw water on the stones, I gave up any pretense of bravery and dived for the floor where the temperature was more bearable.

But I got even a few minutes later when we jumped into the icy lake outside. The water temperature was only 40 degrees, and Erkki howled in dismay as he hurriedly splashed back to shore. Resisting the impulse to follow him, I plotted revenge. Pretending enjoyment, I stood up in the shallow water and dived in again, shouting: "Hey, hey, this is great!" Actually, after that smoke sauna, it was.