July 27, 1986

It is a long, hot summer in New York for David Letterman. First, there is the problem of the Nielsen ratings - they've never been higher. ''It's like a tap on the shoulder from some ominous unknown force,'' said Mr. Letterman the other night after the 5:30 P.M. taping of NBC's ''Late Night With David Letterman'' in studio 8H in the RCA Building, where Toscanini once conducted. ''It's like a warning that I've got to do better, and keep doing better, or the ratings will go down and I'll be left a lonely broken shell of a human - like I am now.'' Then there is the Emmy Award problem: NBC has already announced that Mr. Letterman will be the co-host of the Emmy ceremonies on Sept. 21. ''The way I look at it, they have till mid-September to find someone else for the Emmy deal,'' said Mr. Letterman. ''I'm especially afraid that they'll want me to sing and dance in a large group of people.'' Even more troublesome are the four television specials that NBC has announced he'll be doing next year: ''I hope we don't have to do a one of them,'' Mr. Letterman said. ''I mean, we have our hands full just keeping this thing going every night.''

''A songwriting partnership is like a marriage,'' Richard Rodgers wrote. ''Apart from just liking each other, a lyricist and a composer should be able to spend long periods of time together - around the clock if need be - without getting on each other's nerves. Their goals, outlooks and basic philosophies should be similar, so that the song they create is accepted as a spontaneous emotional expression emanating from a single source.'' Rodgers's comparison of songwriting collaboration to marriage is one of those cliches that happens to be profoundly apt. But while it applies as much today to Broadway collaboration as it did 30 years ago during the golden age of the Broadway musical, the ethics and expectations of theater songwriting, like the institution of marriage itself, have changed and relaxed. It now costs about $4 million to mount a typical Broadway show, and the process of investment and development usually takes several years. Ambitious songwriters have to scramble to become involved in the few projects that eventually get produced on Broadway. And with so much riding on each show, their collaborations tend increasingly to be short-term affairs tailored to specific projects.

It's no secret to say that drama is a restrictive medium, and that those of us who try to write plays are hedged in on all sides by tough laws of dramaturgy which we break only at our peril. To compound the problem, American playwrights, dependent as we are on the uneasy generosity of private enterprise, would seem to be even further encumbered by economic inhibitions that require us to be downright miserly about the number of characters we use or the settings in which our plays take place. Of course, all playwrights everywhere have long been used to dancing in various chains. Aeschylus was bound by the ritual rule that only two characters on stage at one time were allowed to exchange dialogue. Moliere had to be scrupulously tactful about church and court under the shadow of Louis XIV. Samuel Beckett embraces and makes a virtue of the very spareness which good contemporary drama is asked to impose upon itself.

''This isn't a drought,'' Ray Ward, a Georgia dairy farmer, said one day last week. ''It's not even a disaster. It's a catastrophe.''

BEFORE New York's office economy grew as burly as it is today, financial institutions often required developers to have anchor tenants in place before they would write a construction loan for a major new office tower. In the current market, however, an unusual number of major buildings have been started by financially strong development companies without any tenant commitments at all. Perhaps the most notable was 7 World Trade Center, a 47-story, 1.9 million-square-foot office building begun a year ago by Silverstein Properties with no tenant commitment. Drexel Burnham Lambert, the investment house, agreed only two months ago to take an equity interest in the project and also lease the entire building for 30 years. Other major office buildings that have started without major tenants include Olympia & York's 607,000-square-foot building at 425 Lexington Avenue, at 44th Street; Madison Equities's 400,000-square-foot building at 135 East 57th Street, at Lexington Avenue, and a William Kaufman Organization building at 17 State Street near the Battery with 525,000 square feet of space.

THE financial demands of buying the first house are often too great for young people to take on without parental help, normally in the form of a lump sum against part or all of the down payment. But several factors have conspired to create increasing concern over the way this is handled, and the arrangement may require careful structuring. The amount of money involved may be substantial: A 20 percent down payment on even a modest $150,000 house in the New York metropolitan region, for example, comes to $30,000. Even if they were willing to do so, many parents cannot afford simply to hand over so much money as an outright gift.

WITH the international clamor for sanctions, South Africa's white leaders, in a bellicose mood, seem increasingly to be preparing for a siege. ''If we are forced to go it alone, then so be it,'' President P. W. Botha said recently. ''South Africa will not crawl before anyone to prevent it.'' The South African leader seemed to be speaking from a position of economic and military strength in a region of frailty and dependence among black-ruled neighbors. Yet some analysts argue that strength may prevail only while the nation's 4.5 million whites, a minority that has been ruling for six weeks by emergency decree, secure the quiescence and division of the restive black majority, more than 23 million people. If Pretoria's grip is to falter, this theory holds, it will be weakened from within by an ethnic arithmetic that outstrips the slow-motion racial and political changes. While the black population, here as elsewhere in Africa, is growing at a rate the economy can barely sustain, white emigration is building, particularly among young professionals.

CHINATOWN: Restaurants, apartments and curio shops jumbled along narrow streets? Not for long. This city's Chinese-American community is about to expand into brand new modular quarters that will make it the most modern Chinatown in the country. It is the idea of the Chinese-American development Corporation, a private for profit corporation, working closely with the city. It is buying 30 acres of adjacent vacant land, directly north of the current Chinatown, for $7.2 million. The site was a Sant Fe railyard that was leased to Amtrak until two year ago, said Ping Ton, president of the development company.

President Reagan plans to renew a year-old ban on the export of some goods to South Africa and may send a special mission to warn the Pretoria Government that unless it speeds political change, stiffer penalties will follow, a ranking Administration official said today. The mission, in the form of a special envoy or a group of legislators, would be intended to caution South Africa about Congressional pressure for more serious economic sanctions. The official said the President wanted to make sure the South Africans understand the position in which the Administration finds itself. U.S. for Talks With Guerrillas The United States is seeking the release from prison of Nelson Mandela, the black leader, the start of a dialogue between the South African Government and the African National Congress, the black guerrilla group, and further easing of apartheid.

Near midnight Friday, Marvis Frazier, in sweat clothes, stepped out the door of the Queensbury Hotel here and went for a run of a mile and a half. Based on what happened in the ring at the Glens Falls Civic Center today, Frazier should have kept going, due west to his hometown of Philadelphia and out of harm's way. For Mike Tyson, the undefeated heavyweight, showed no respect for the fighting Frazier name. With an explosive opening barrage of punches, he knocked out Frazier, the 25-year-old son of Joe Frazier, the former heavyweight champion, at 30 seconds of the first round of a scheduled 10-round bout.

SELDOM has it been harder to read the United States economy. Analysts say that some some recent measurements looked awful, some appeared strong and others were just plain puzzling. The Government reported last week that the nation's output of goods and services rose at an annual rate of 1.1 percent in the second quarter. At the same time, it raised the growth rate for the January-March quarter to 3.8 percent from the 2.9 percent calculated earlier. The gross national product thus grew at a rate just under 2.5 percent for the first half of 1986 - not quite satisfactory, most economists maintain, but not cause for alarm. The G.N.P., however, has become an increasingly unreliable indicator of overall economic health. It is not that Government statistics-gathering is at fault - though frequent revisions are evidence of the limitations of the craft - but rather that the 44-month-old recovery has become badly lopsided. Manufacturing, oil exploration and much of agriculture and commercial real estate are all statistically flat on their backs. But home building, financial services and much of retailing are booming, the numbers tell us.

WHEN, in August 1929, the art critic Thomas Earp adversely criticized both D. H. Lawrence's introduction to a catalogue of his paintings, and the paintings themselves, Lawrence wrote and published the following poem: I heard a little chicken chirp: My name is Thomas, Thomas Earp! And I can neither paint nor write I only can set other people right. All people that can write or paint do tremble under my complaint. For I am a chicken, and I can chirp; and my name is Thomas, Thomas Earp. How good a weapon is literature for settling scores with someone by making his person or art an object of ridicule? To what extent can we adequately ac-count for a poem, story or novel by locating its origin in spiteful feeling, a determination on the author's part to celebrate - with humorous zest or steely-eyed contempt - the offenses of another?