They were having a quiet summer festival last week in Kotka, a seacoast town on the road between Helsinki and the Soviet border.

Couples sat under striped tents, drinking beer and eating bratwurst. Families strolled through the main park, past rose beds, fountains and freshly painted benches as a sea of blond heads listened raptly to a band playing cool jazz. No one spoke or hummed, let alone tapped a foot.

There is a certain stillness about Finland that foreigners find almost eerie. It is as if 4.9 million Finns had settled into a state of unanimous serenity.

Homogeneity has something to do with it. The population is 89.8 percent Lutheran, 93.6 percent Finnish-speaking and overwhelmingly blond.

BUT THIS is also a country of the happy medium. Helsinki is an attractive capital of almost half a million, not too big, not too small. People are reserved but pleasant, efficient without being officious. Restaurants are crowded, but there is almost always a table free.

Street life here is modulated. Finns, like Russians, do not jaywalk; they wait for the green light to cross an empty street. Even the punk crowd wears fashionable pastels.

Politically, people agree that the country has reached a consensus. Minor parties have joined in the competition for the average voter; ever fewer are left on the fringes.

Even the rural party, once considered a party of protest, mellowed once its head was invited to join the coalition government.

As it is, Finland spends less on the public sector than some of its Nordic neighbors and controls 16 percent of industry. In terms of standard of living (or per capita gross national product), it ranks behind Sweden and Norway but ahead of France and Japan.

The national sense of well-being and of pride at successfully mixing socialism and capitalism was evident in comments made by Kalevi Sorsa, the Social Democratic prime minister, to foreign bankers and investment analysts last year.

"Can you please name a country where market forces operate so freely as to frighten some firms, where there is no international terrorism and never has been, where prayer in the schools has been part of daily life for decades," he said. THE PERVADING harmony has reached the point where articles have appeared lately asking whether a little disagreement now and then might not be a good thing.

Even the Communist Party, split philosophically between pro-Moscow and Eurocommunist camps, is hard-pressed to challenge the status quo, since its main issue -- relations with the Soviet Union -- was long ago coopted by the consensus.

In the past decade, politicians of practically all persuasions have come to share the view that Finland is better off promoting good relations with its giant neighbor. If that has meant muting criticism of the Soviet Union, most figure it is a small price for independence.

In the 1960s, Finland's unique relations with Moscow gave rise to the term "Finlandization," a concept used in Western Europe to warn against crippling neutrality and gradual loss of autonomy.

The pejorative use of the term brought protests from Finnish embassies, and now it is heard less often. But for many Finns, the accommodations with Moscow are easily defended.

Finland lost a war against the Soviets and shares a border 762 miles long with them. Furthermore, trade with the Soviet Union is a key factor in protecting the Finnish economy from the buffeting of western recessions.

The 10th anniversary celebration last week of the signing of the Helsinki human rights accords was an affirmation of success at balancing between East and West.

"For Finland, it has been a natural principle in a divided world to deal with all sides, to be open in all directions, to show others the confidence that we hope others will show us. This is our policy of neutrality," said President Mauno Koivisto at the opening ceremonies.