July 19, 1981

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.