April 11, 1982

Henry Willets Underhill regrets that he ever agreed to sell 81 acres of a 200-acre Jericho, L.I., farm that his family had held since 1793. Mr. Underhill was persuaded that the scenic beauty of the land would be preserved when it was developed. But the plans now call for leveling a hill and filling in seven ponds to accommodate 220 single-family houses.

President Elias Sarkis met with the Ambassadors of the United States and the Soviet Union today and reportedly appealed for their intervention to stave off a feared Israeli invasion. Contributing to the heightening of tension here were reports of Israeli troops movements near the border, continued Israeli threats of reprisals for the slaying last week of an Israeli diplomat in Paris, a reported regrouping of Syrian forces in Lebanon, and reports that the Palestine Liberation Organization has put its guerrilla forces on maximum alert. ''We are doing our best to urge maximum restraint on all sides,'' the United States Ambassador, Robert Dillon, said after his meeting this morning with President Sarkis. Mr. Dillon said Washington was in touch with the Israeli Government and the other governments in the area over the situation in Lebanon. 'Very Serious,' Russian Says The Soviet Ambassador, Aleksandr A. Soldatov, said after his meeting with President Sarkis that the situation in southern Lebanon was ''very serious.''

We are living in a most peculiar musical age. Musical life is booming, audiences are growing, seasons are expanding, conservatories are turning out virtuosos. In New York, well over a hundred concerts are given every week. There is an extraordinary bustle and whirl in the music world and its accompanying business. But in the midst of all that activity, there is a certain stillness, an immovable center. For our musical life is based upon repetition. In recent weeks, for example, the New York Philharmonic and the Metropolitan Opera have announced their programs for the coming season. At the Philharmonic, there are, of course, some unusual offerings. A concert performance of Janacek's ''From the House of the Dead'' is planned as are programs devoted to Shostakovich and to the Polish modern, Witold Lutoslawski - all reflecting growing interest in Slavic and Eastern European composers. There is also a ''retrospective'' of six compositions by Schoenberg planned, concentrating on his earliest music.

BRIDGEPORT AS most of Connecticut's hundreds of thousands of Protestants and Roman Catholics gather for joyous Easter services and festive dinners today, an often somber Holy Week is beginning for the 300 parishioners of St. Dimitrius Rumanian Orthodox Church here. Tonight, the Rev. Dimitrie Tatulescu will hang the purple drapes, symbol of the mourning to come, in the church. In many homes, families will eat lentil soup or tarapaschi, the traditional corn porridge, in keeping with the Lenten prohibition on meat and dairy products. Some women will be buying lamb, walnuts and feta cheese for the Easter feasts to follow. And congregants from as far as Hartford and New York City, and perhaps a relative or two from the old country - all bound by their roots in the Macedonian region of southern Rumania and northern Greece - will be planning the journey to the Clinton Street church.

THE brand managers at XYZ multibillion-dollar packaged-goods companya reconvinced that the company's new product is the best thing since sliced bread. The hotshots on Madison Avenue think they've created an unforgettable advertising campaign. Everybody is keen on sending his particular banner up the proverbial flagpole. But will anyone salute? To answer that all-important question, companies engage in an often expensive, lengthy and frequently inconclusive exercise known as test marketing, in which they try out their new product or marketing program in a handful of towns that mirror, as nearly as possible, the demographics and buying patterns of the nation. It is an effort to determine not merely how a product or marketing strategy will play in Peoria - itself a popular test-market town - but, based on Peoria, how it will be received nationwide. Because a national introduction may involve outlays of millions of dollars, test markets are a safety net under mass-marketers' slender highwire.