Last week, while the Metropolitan Opera was singing in Washington, the Finnish National Opera took over the Metropolitan's home in Lincoln Center. It was the first time the Met has acted as host for a visiting opera company.

The visitors had a double-edged challenge: unfamiliar, contemporary operas sung in Finnish, a language almost impenetrable to non-natives. Yet they communicated powerfully.

The two operas presented--"The Last Temptations," by Joonas Kokkonen and "The Red Line," by Aulis Sallinen--both have strong atmosphere, full of the harshness of peasant life in a cruel northern climate and the abrasive social interactions of a nation of individualists.

In Finland, "The Last Temptations" has the kind of popularity that in this country is enjoyed only by a few repertory standards like "La Bohe me." It has been continuously in production since its premiere in 1975 and is the cornerstone of the nation's strong contemporary operatic repertoire. "The Red Line," composed three years later, is marginally more accessible for non-Finnish audiences on a first hearing. As presented in New York last week, both productions were music theater experiences of the highest quality.

The Finnish National Opera is the only professional opera company in Finland--a small country and not particularly affluent. Unlike most American companies, it has made a special effort to develop new repertoire related to the lives and interests of its audiences. In terms of theatrical values and potential mass-audience involvement (though not of musical idioms), "The Last Temptations" and "The Red Line" demand comparison not with "Don Giovanni" or "La Traviata," but with the kind of musical theater that middle America has taken to its heart--such shows as "Evita" and "Fiddler on the Roof."

Like "Evita," "The Last Temptations" is the story of a controversial, charismatic, historic figure, told in a series of deathbed flashbacks. The figure is Paavo Ruotsalainen, a backwoods evangelist of the 19th century. It is a story of struggle, not only against the religious establishment of his time (which he shook to its foundations), but against killing frosts, grinding poverty, the misunderstanding of family and neighbors, and--at the end, in the last temptations--the specter of despair: the fear that his life has been meaningless, that he has neglected home and family for pride or for an empty dream.

In one powerful scene, Paavo's wife tries to stop him as he is leaving on a preaching expedition. "That's the last loaf," she shouts as he stuffs bread into his knapsack. "Surely the Lord will look after his own," he answers, and she throws an ax at him, missing but leaving a mark on the door post for the neighbors to gossip about in the next scene.

Even with fairly frequent moments of high tension, "The Last Temptations" is essentially metaphysical drama. Kokkonen has recognized the special need for verbal clarity in this work and developed a vocal style of continuous melody, closely adapted to the natural speech rhythms of the Finnish language. Hymn tunes are used with strong dramatic effect.

"The Red Line" is more theatrical. Like "Fiddler on the Roof," it is the story of peasants struggling in the grip of historic forces that they do not really understand. The village is near the Russian border and it is terrorized by a bear--"symbol of a hostile nature," according to a Finnish program annotator who does not mention Finland's neighbor, the Soviet Union, as another possible interpretation.

In the opening scene, Topi, a peasant, comes home with a bit of wool and a bell--all that remains of a sheep killed by the bear. "In the forest sleeps a bear stuffed with meat," cries his wife, Riika. "In the home, the children are hungry as wolf cubs." Before the opera's end, Topi's three children die of starvation, and in the last scene (offstage), he is killed by the bear he has sworn to destroy. Despite this depressing plot line, the effect of "The Red Line" is largely one of vitality and optimism.

"The Red Line" also deals vividly with the election campaign of 1907, bitterly contested between the Social Democrats and a conservative party with clerical overtones. Some of its finest scenes show peasants trying to come to terms with the new idea of democracy. Topi, who has never held a pencil in his life, wonders whether he will be able to mark his ballot properly. The music is vivid, sometimes quite Russian in flavor and very effective in its use of folk idioms--particularly a riddle song in the first act and a haunting lullaby (which is also a song of mourning) in the second.

Both composers handle the orchestra with special expertise, making frequent, vivid instrumental commentary on the action, amplifying and intensifying the meaning of the vocal music. This helps to minimize the language barrier, and so does the highly developed acting ability in both productions.