What was going on when I was born?

THE LAST LAUGH By S.J. Perelman. Introduction by Paul Theroux. 192 pp. New York: Simon and Schuster. $12.95. S.J. PERELMAN, it turns out, left behind four chapters of an autobiography when he died in 1979. He planned to call it ''The Hindsight Saga,'' a perelmaniacal spin off ''The Forsythe Saga.'' These bits of memoir, published for the first time in ''The Last Laugh,'' are the tailpiece to a collection of 17 of Perelman's comic sketches for The New Yorker. Even in its fragmentary state, ''The Hindsight Saga'' strikes me as the best thing Perelman ever wrote. So much so, in fact, I can't help but wonder why some editor, somewhere along the way, didn't take El Sid, as admirers sometimes called Sidney Joseph Perelman, by the back of his custom-collared neck and push his nose and the round-rimmed spectacles on the bridge above and the Cold Stream Guards thatch on the lip below into this sort of material long ago.

WASHINGTON FOR two days last week, Senator Harrison A. Williams Jr. sat in a Senate hearing room and witnessed a rerun of the taped evidence that led to his conviction on May 1 of Federal bribery and conspiracy charges. At stake is his 23-year career as a member of the Senate. Mr. Williams, Democrat of Bedminster, will return on July 28 to give his side of the Abscam story to the Senate Select Committee on Ethics. If he is unable to convince his peers that he has not disgraced his office, he could be the first United States Senator to be expelled since the Civil War.

Israel last week carried its policy of pre-emptive/retaliatory strikes against Palestinians into the heart of Beirut, demolishing buildings that housed guerrilla headquarters as well as hundreds of civilians. The Lebanese Government said 300 people were killed and 800 wounded in the raids on the Lebanese capital and in the south of the country, where Israel bombed launching ports for guerrilla strikes and also destroyed bridges that served as supply links for civilians and guerrillas alike. The raids followed the deaths of three Israelis in the Mediterranean resort of Nahariya during intensive Palestinian rocket attacks across the Lebanese border. Menachem Begin, newly re-selected as Prime Minister, said Israeli forces would ''not intentionally'' attack civilians but would not be deterred by their presence from attacking guerrillas.

The astonishing wave of what some Britons called ''copycat'' violence spread to 30 cities before subsiding last week. And then police officers searching for a gasoline bomb factory busted their way with sledgehammers into 11 houses in Brixton, a racially mixed London neighborhood in which riots had erupted in April and again two weeks ago.

-------------------------------------------------------------------- SARAH FERRELL is an editor on the staff of the Travel Section. By SARAH FERRELL By and large, the Borromeos are a lucky lot. Over the centuries the family has been rich (banking), powerful (politics) and certifiably pious (St. Charles Borromeo, whose relics are in Milan Cathedral, was one of their number). Perhaps best of all, they have, since the 12th century, been the proprietors of the Borromean Islands, a handful of tiny specks of land afloat in northern Italy's Lake Maggiore, within sight of the bustling resort town of Stresa. Of the three major islands (insofar as anything so small can be major), two - Isola Madre and Isola Bella - remain Borromean domains, although the Borromeos will let tourists play on them. The third, Isola Superiore, better known as Isola dei Pescatori, is now part of the Commune of Stresa, but fishermen lived here as long ago as Neolithic times and established effective ownership long before the Borromeos arrived.

WESTBURY FLEA markets offering discount merchandise are continuing to proliferate throughout the Island, vying with established retailers for billions of consumer dollars. Thousands of shoppers are thronging the markets at Roosevelt Field, Commack, Smithtown, Huntington Station, Valley Stream, Republic Airport in Farmingdale and Belmont and Aqueduct Race Tracks, among other places, to browse, buy and seek out bargains in an often carnival-like atmosphere. While flea markets once sold an eclectic mix of antiques and laterday wares (now called collectibles), today the emphasis is on brandnew, brand-name merchandise, running the gamut from designer jeans to sneakers, jewelry, cosmetics and housewares. Hard goods and soft goods share stall spaces with purveyors of sour pickles from the Lower East Side, dried fruits and nuts and ''fresh-baked'' apple strudel. Some flea markets impose a parking fee or an admission charge for the privilege of shopping. ''The flea markets are hurting the merchants in the old downtown areas, and they are beginning to hurt the shopping centers also,'' said Roy N. Cacciatore, Commissioner of Nassau County's Department of Commerce and Industry.

W ILL the sleek A320, the blunt-nosed MDF-100, the porpoise-snouted 7-7 all use the new PW2025? Will they also employ the revved-up CFM56-2000? And the redirected RJ500? Or will any of them come to market at all? The alphabet soup that drenches the jet engine manufacturing industry these days has an engagingly zany, science-fiction ring. But the shorthand is for a nervously competitive situation frought with potential for profit -and for penury. The three main makers of engines for the free world's commercial jetliners have begun jockeying in the preliminary phase of what they call ''the next big engine battle'' - the competition to equip perhaps 2,500 new-model, fuel-efficient, 150-passenger jetliners that are expected to be built in the later 1980's and the 1990's. ''We've got to deliver the better mousetrap,'' Dennis A. Head said doggedly in a recent speech. As managing director of operations for London-based Rolls-Royce Ltd. (the RJ500 engine), he is with one of the three competitors hoping to put a lock on the power source for the new jets. On the American side are Pratt & Whitney Aircraft (the PW2025) and the General Electric Company (the CFM56-2000).

HARTFORD THE General Assembly passed 547 bills in its last session, of which Governor O'Neill approved all but 15. When the legislators return to the Capitol tomorrow, they will have a three-day limit for debating and acting on the 15 vetoes, but they are planning a session of only one day. With only three bills of broad interest facing review by the General Assembly, some members think the session will take substantially less than a day. The three bills would raise unemployment compensation benefits in the next five years higher than the limit set by the existing law; bar investment of state pension funds in corporations doing business with South Africa, and establish one-way tolls in some places on the turnpike and parkways.

-------------------------------------------------------------------- DAVID TABACOFF, a news producer for ABC television, lives in New York. By DAVID TABACOFF We arrived in Jogjakarta at dawn after a tiring 16-hour trip from Bali by bus and ferry. My wife, Sheri, and I had come to the town in central Java to visit its renowned batik factories and to see the ruins of a nearby Buddhist shrine called the Borobudur, described by some travelers as the Parthenon of the East. But all we wanted to do at that moment was to get some sleep. As we stood on the street with our luggage, exhausted and anxious, someone spoke to us in English: ''What is your program?'' The questioner was a small, wiry bicycle-rickshaw driver. Our program? All we knew was that we wanted to find an inexpensive, but clean and comfortable, place to stay. ''I can take you there,'' the man said with assurance. After a few weeks in Asia, we were wary of such comeons, but we were so tired that we overcame our reluctance and piled our luggage and ourselves into his rickshaw and headed off.

INTERRACIAL adoptions, which reached their peak in the late 1960's, are waning, particularly in nonintegrated areas of the Island. Adoption agencies are attempting to find black homes for black children, who far outnumber the white children available. Little Flower Children's Services of New York, the second largest residential children's agency in the state, with 1,600 children at facilities in Wading River and Brooklyn, has announced a campaign for black children from infancy to 17. According to Angela Hazel, a case worker, 14 blacks are available through the agency, and 48 more are in the legal process of being freed for adoption. ''Unless a child is so hard to place that we have no choice,'' Mrs. Hazel said, ''we will not place black children in white homes. The ideal home for children is a home of their own ethnic setting.''

VALHALLA AN inch of water stood on the flagstone floor of the entrance to the County Jail here during the recent riots as a Corrections Department van pulled up. More than 500 county and state officers in riot helmets, flak jackets and armed with shot guns stood guard in the hot night. The van door opened. Television lights quickly went on, supplementing the mobile floodlight units summoned for the emergency from surrounding communities. Reporters at the jail entrance peered inside the van.

Bill Rogers shot a three-under-par 67, his second consecutive sub-par round, and extended his lead in the British Open golf championship to five strokes today. While Tom Watson, Jack Nicklaus, David Graham and Ben Crenshaw floundered out of contention on the 6,829-yard Royal St. George's course, Rogers finished 54 holes with a score of 205. He was the only player under par for the tournament in the 81-man field, which was cut to the low 61 for tomorrow's final round. Bernhard Langer of West Germany, who scored 70, and Mark James of Britain, 68, shared second place at 210. It was expected that only a hot round from someone like Raymond Floyd, who was tied for third with Isao Aoki at 213; forecasted foul weather, or frazzled nerves would keep Rogers from his first major title.