September 10, 1985

The triumphant researchers who found the luxury liner Titanic were greeted at their home port here today by cheering crowds, balloons and the blare of airhorns. Two helicopters and a flotilla of little boats followed the 245-foot Navy research vessel Knorr to her landing as the exhausted discoverers waved to families, friends and hundreds of reporters from around the world. ''I'm glad it's over,'' Dr. Robert D. Ballard, leader of the research team and a senior scientist at the Woods Hole Oceanographic Institution, shouted from the deck as the Knorr pulled up to the institution's wharf. The first man to shake his hand was Rear Adm. J. B. Mooney Jr., Chief of Naval Research. The Navy financed the development of the underwater robot sled Argo, which last week took more than 12,000 photos of the liner, which sank 73 years ago with the loss of more than a thousand lives. The Navy wants to use the Argo for top-secret military missions, according to naval sources and scientists who work for the Government.

Federal regulators refused today to block the trucking of spent nuclear fuel through New York City. The regulators, from the Department of Transportation, acted in a case brought by New York City, which claimed that the city's dense population made it unsafe to move the radioactive material through Queens and the Bronx. Officials in Connecticut were jubilant over the decision because they had feared that the nuclear material would be detoured through their state if New York City had won its case. ''We've taken a little bite out of the Big Apple,'' Joseph I. Lieberman, the Connecticut Attorney General, told a news conference in Hartford.

''Our influence over South African society is limited. But we do have some influence, and the question is, how to use it.''

EARLY tomorrow, as the climax of an extraordinarily audacious and complex series of space acrobatics, a small spacecraft will plunge through the tail of the comet Giacobini-Zinner. The mission, by the International Cometary Explorer, will be the first to a comet and will provide a dress rehearsal for the multiple fly-bys of Halley's comet next March. During the precious one or two hours of its passage through the tail, radio observatories from Japan to Spain will seek to record transmissions from the spacecraft as it makes the first direct observations of the comet's composition, magnetism and other properties. Spacecraft have visited the Moon, analyzed the soil of Mars, passed close to the great outer planets, their moons and rings. Meteorites of diverse types are in our museums. But until now we have never had a close look at a comet.

Even though car and truck sales will hit record levels for the 1985 model year, the chairman of General Motors Corporation warned today that the American auto industry, and others as well, would have to move swiftly to computerize their operations to meet threats from abroad. Roger B. Smith predicted that total American sales of cars and trucks -domestically made or imported -would reach 15.4 million by the end of the month, which is the end of the 1985 model year. The previous record was 15.3 million in the boom year of 1978. And he said he expected 1986 to be strong as well, though perhaps not reaching a record. ''We have a real shot at surpassing 15 million units again,'' he said at a news conference.