What was going on when I was born?

The Lebanese Army today began tearing down the Green Line, the five miles of barricades that divided the Moslem and Christian sectors of Beirut and seemed a symbol of the long civil war. Large earth-moving machines worked all day to remove mountains of sand, wrecked cars, lampposts and broken furniture that had been piled up by militiamen as fortifications. The clearing of the Green Line, which ran from the sea at the northern end of Beirut to the southern suburbs, was aimed at reunifying the city and bringing it under the authority of the Government of Prime Minister Rashid Karami. The clearing was without incident.

The New York Court of Appeals ruled yesterday that under a state law designed to encourage housing construction, the developer Donald Trump is entitled to a 10-year tax abatement for the Trump Tower on Fifth Avenue. In a unanimous decision, the court, the state's highest, ruled that the law applied to luxury apartment complexes as well as lower-income projects as long as they were constructed on ''underutilized'' property. The 59-story Trump Tower, where one-bedroom apartments sell for $500,000, is at 57th Street and Fifth Avenue, the former site of the Bonwit Teller department store. ''The Legislature did not choose to restrict availability of this exemption to construction of low- and middle-income housing,'' Judge Judith S. Kaye wrote for the court. ''Thus, it is immaterial that luxury housing is at issue.''

The Berkshires, one of America's premier resort centers, can be a lovely drive from the metropolitan area, up the scenic Taconic State Parkway and east on Route 23 through the dairy country of Columbia County, into Great Barrington, Stockbridge and Lenox, Mass. In addition to its magnificent scenery, charming inns and picture-book New England towns, the Berkshires area is a magnet in summer for music, theater and dance fans. But a word of caution: Precisely because it is a major tourist area, it is crowded in the summer, especially on weekends. There may be traffic jams in and around the attractions, and it is often hard to find a parking space in the center of town. Perhaps the most famous music festival in the country, Tanglewood, summer setting for the Boston Symphony Orchestra, has just opened its 56th season in Lenox. The program tonight at 9 features Isaac Stern as

Friday NEW LONDON SAIL FESTIVAL At the annual Sail Festival this weekend on the banks of the Thames River in New London, Conn., visitors can dance, eat, shop and watch the acrobatics of windsurfers and parasailers. At 3 this afternoon, at the Thames River Yacht Club, sailors will set out on one- and two-day races at sea. Downtown New London will be filled with flea markets, craft shows and entertainment. Fireworks tomorrow night can be seen from City Pier or from across the river at Groton's Fort Griswold. It's all free, but tickets for a fireworks- starlight cruise with commentary by George Plimpton are $17.50. The boat leaves the Block Island Ferry Slip tomorrow at 8. Interstate 95, Exit 83, or Amtrak or Greyhound, a two-hour trip from New York. Anchorages for boaters: (203) 443-8331. FIDDLERS FOUR IN TRIBECA Jay Ungar likes folk dances, Matt Glaser writes about technique and Evan Stover accompanies the composer-musician David Bromberg on the guitar. But when they get together, they just fiddle away. Their group, Fiddle Fever, which ranges from Celtic ballads to swing, will be at the Alternative Museum, 17 White Street at Avenue of the Americas in TriBeCa, tonight at 8. Admission, $7. No. 1 train to Franklin Street, or A or E to Canal Street. Information: 966-4444. GRACE CHURCH SING

Delegates to the Democratic National Convention narrowly prefer Senator Gary Hart over Representative Geraldine A. Ferraro as a running mate for Walter F. Mondale, a survey by The New York Times shows. But when the figures for Mrs. Ferraro and for other individual women were added to the percentage of delegates who said Mr. Mondale should pick ''a woman,'' the total outdistanced Mr. Hart's. The Colorado Senator, who provided Mr. Mondale's most dogged competition in the primary campaign, was preferred by 23.5 percent of the sample of 1,166 delegates surveyed. Mrs. Ferraro, the Queens Democrat who has emerged as the leading choice of delegates urging Mr. Mondale to pick a woman, was backed by 18.5 percent. Survey Signals Support The breadth of support for a woman on the ticket was demonstrated by the fact that an additional 12.1 percent of the delegates either named another woman or simply said that Mr. Mondale should pick a woman.

New car sales by the major American auto makers continued strong in the last 10 days of June, finishing 10.9 percent ahead of robust sales at the same time last year, the companies reported here today. The selling rate during the period was the highest since 1978. Sales for all of June were up 8.9 percent for the major domestic producers, putting the seasonally adjusted annual selling rate at 8.3 million, compared with 7.5 million for last June. Held down by the recent metalworkers' strike in West Germany and supply problems in Japan, imported car sales slipped 4.1 percent in the month, to 223,690 units, from 233,205 last year. That resulted in an annual rate of 2.6 million, the same as last June.

This summer, as in summers past, farmers' hopes for a prosperous year grow with their crops. But for the makers of farm tractors and combines, the hopes for a turnaround in sales have been dashed, and they are cutting back again. Last month, for example, Deere & Company, with excessive inventories on hand, said it would lay off 600 workers at its plant in Waterloo, Iowa. International Harvester will keep the gates of its tractor plant in Rock Island, Ill., locked until mid-August, extending the normal vacation shutdown for three weeks. And it will suspend combine production for the month of September. Other manufacturers are making similar adjustments.

Decision excerpts, page B6. WASHINGTON, July 5 - In a victory for the Reagan Administration's position on a key controversy in criminal justice, the Supreme Court today ruled that some evidence obtained with defective search warrants could be used by the prosecution in criminal trials. The decision allows a narrow exception to a 70- year-old rule that attempts to deter police misconduct by excluding the use of illegally obtained evidence. The Court held that the rule should not apply when the police act in ''objectively reasonable reliance'' on a search warrant that at the time appears to be valid, even though it later proves defective. ''Application of the extreme sanction of exclusion is inappropriate'' under such circumstances, Associate Justice Byron R. White wrote for the Court. The 6-to-3 decision, announced on the final day of the Supreme Court's term, was a major victory for the Reagan Administration.

An article in Business Day June 23 about the National Bank of Washington, owned by the United Mine Workers of America, incorrectly described the extent of bank ownership by major unions. A second such bank, the Amalgamated Bank of New York, is owned by the Amalgamated Clothing and Textile Workers Union.

He is one of the last of the Old Bolsheviks, a trusted lieutenant of Stalin, living in obscurity since he fell from power 27 years ago. Today a Soviet official confirmed that Vyacheslav M. Molotov, Prime Minister and Foreign Minister under Stalin, had been reinstated on the Communist Party rolls at the age of 94. Mr. Molotov was dismissed from the leadership in 1957 by Nikita S. Khrushchev for having been part of a so- called antiparty group that sought to unseat Mr. Khrushchev. After Mr. Molotov had been relegated for five years to minor diplomatic posts, Mr. Khrushchev sent him into retirement in 1962 and had him ousted from the party, which Mr. Molotov had joined as a teen-ager in 1906.

''The internal military situation is perfectly normal. Democracy has in no way even been grazed.''

Healthdyne Inc., a glamour stock that climbed to a high of 40 3/4 just over a year ago only to slide to 6 3/4 today, has work to do on several fronts if it is to regain favor on Wall Street. But the most pressing problem is finding a president. The company was founded in 1970 by Parker H. Petit to develop a monitor to protect children susceptible to crib death, or Sudden Infant Death Syndrome, after his son died from the mysterious affliction. He brought in his former colleague and longtime friend, James E. Ashton, 41 years old, to be the president and chief operating officer last December, only to have a falling out. The clash culminated in Mr. Ashton's dismissal effective next Sunday, less than seven months after he joined the company.