What was going on when I was born?

WESTBURY IT is normal for indicted politicians to express confidence that they will be vindicated. But Joseph M. Margiotta, the Nassau County Republican Party chairman, is acting like a man who is almost certain he will be exonerated. Mr. Margiotta has made almost a political and family outing of his trial on mail fraud and extortion charges in Federal District Court here. The 53-year-old Republican leader is charged with depriving Nassau County and the Town of Hempstead of honest government by presiding over a system in which $500,000 in municipal insurance commissions was dispensed over a 10-year period to politicians designated by Mr. Margiotta for little or no work. Mr. Margiotta was a somber figure - his face a mask of resignation -when the trial opened nine days ago with the selection of the jury. But his demeanor has changed since the testimony began last Monday. He frequently looks into the audience and smiles at friends and relatives from his position at the defense table, where he is flanked by as many as five lawyers.

STONY BROOK ''WHAT'LL it be tonight -turbot with fruit sauce or veal Parmesan?'' asked Arlene Nekrutman, the effeverscent manager of the Roth Cafeteria, one of the three main dormitory dining rooms at the State University at Stony Brook. The student, who wasn't familiar with turbot, a firm-fleshed white fish, was offered a taste. ''Not bad,'' he said, ''but I think I'll have the veal.'' For students attending colleges and universities on the Island, where and what to eat can be perplexing and often frustrating. As food costs skyrocket, attempting to satisfy students' palates and pocketbooks also presents problems to the purveyors. With more than 129,000 students on Long Island campuses, supplying several meals and snacks each day has become a big business. At Stony Brook, where more than one-third of the student body lives on campus - approximately 6,000 of 16,000 - more options of what, where and how to eat are available than at most other schools on the Island.

IN= the end, the familiarity of it all was the most dreadful. The shots, the shock, the screams, the Secret Service scramble to pack the stunned President into the limousine readying to rocket away, the affably serious doctors addressing anxious reporters in a makeshift hospital press room, the videotape over and over again that night, the columns in the next days on the when, why and how of American assassins - but above all, the fact that such a fact no longer astonishes. On Monday, March 30, at 2:25 P.M., John W. Hinckley Jr., a 25-year-old well-off dropout, tried to kill Ronald Reagan. The President had been in the Washington Hilton Hotel, selling his economic program to building trades unionists. Outside the narrow Presidential exit - built to Secret Service specifications - he turned to wave to the crowd, some press, mostly curious passers-by, that always gathers near a President. Mr. Hinckley fired six shots with a .22-caliber revolver loaded with explosive bullets called Devastators.

Consider the playwright cursed by the burden of memory, wounded by the pain of the past. Think, for example, of Eugene O'Neill. Old ghosts coursed his brain - scuttling up a synapse, running down a neuron, and hurling themselves onto the stage. Ah, misery! Oh, art! It is how we defined O'Neill. Now consider Neil Simon, who also dredges around his past. He exorcises old ghosts; sometimes he wrestles with demons, but for him they come out funny. For him they make us laugh. Him we define by the calcium deposit in his neck. It is an accretion built up by sitting hunched up over a typewriter, five hours a day for 30 years. Is this fair? Is this just? Where is the artistry and anguish in a calcium deposit? No matter; Neil Simon defines himself by the calcium deposit, too.

IN the language of statistics and econometrics, the attempt to assassinate President Reagan last week represented the movement of a ''random variable'' - a chance element that affects the economy in an unpredictable way but is unlikely to change its fundamental course. Random events are supposed to cancel each other out - unusually bad weather will be offset by a spell of unusually fine weather, the damage of an unexpected strike, like the current one in coal, by the eventual recovery from the strike, and the initial shock to confidence of the attack on the President by the gain in confidence from the recovery of the President. But are the shocks of the real world necessarily symmetrical and evanescent? From period to period, a random variable can assume an infinity of values, ranging from enormous to insignificant, from long-lived to momentary.

Construction workers in wool hats and sweaters unloaded a flatbed truck piled high with slabs of sheetrock. While a demolition crew chipped away old plaster, tilemen at 170 Parkside Avenue in Flatbush laid new floors, and residents carefully sidestepped mounds of sand and mortar. ''When the landlord told us about all the changes, I said I'd believe it when I see it,'' said tenant Rose Steed. ''Now, I'm a lot more confident.'' Mrs. Steed's apartment is in the first New York City building to begin construction under a Federal rent-subsidy program for moderate rehabilitation.

UNTIL three years ago a motel on the East End was a place where travelers with car trouble spent the night, vacationers changed into bathing suits or friends met for the afternoon. Now, however, a growing number of motels are being converted into exclusive residential condominiums and cooperatives, some of which may be used for year-round occupancy. The trend, emerging in the midst of economic pressures that have seen many motels in this popular resort area go into the red - together with the steady demand for real estate, particularly in the Hamptons - raises a number of questions concerning the desirability of the conversions. On the positive side, town planners feel that the conversion of failing motels in residential or business areas is desirable and may upgrade real-estate values. The same planners nevertheless say that conversion of motels along the much sought-after ocean and bay fronts may be detrimental to the multimillion-dollar tourist industry because it will reduce the number of motel units available to transients.

Diplomatic sources said today that Soviet leaders had refused to discuss the Polish situation with Hans-Dietrich Genscher, the West German Foreign Minister, who has just ended a three-day visit here. ''Their refusal is consistent but ominous, especially when they were talking to a man of high rank,'' a senior Western analyst declared. There were hints from Western intelligence officers that a Soviet military buildup around Poland was accelerating. Asked whether there were activities beyond last night's disclosure that Soviet helicopters had been airlifted into southwest Poland, an intelligence source replied in the affirmative, but refused to supply any details.

DEPENDING on where they live, some residents of Islip Town pay under $3 a month for garbage pick-up while others pay more than $8 for the same service. Some get to deduct the cost of collection from their income tax because they pay for the service through their property taxes, while others cannot do so because they pay the private carters directly. This latter group, in addition, must pay sales tax. Spurred by the need to expand its recycling program, Islip Town is moving to make the system and costs of garbage collection uniform throughout the town, and hopes in the process, according to Thomas J. Hroncich, environmental commissioner, to cut both town taxes and the cost of pick-up to many homeowners. But with the major exception of Hempstead Town, much of Oyster Bay Town and most incorporated villages, where municipal employees pick up garbage, the garbage collection system for much of Long Island is shot through with inequities similar to those that exist in Islip. The reason for this is that the collection of garbage and refuse on the Island is handled in a manner far different from other essential municipal servicies. For the most part, it is done by private carters who control given neighborhoods although they have never bid for them, and whose fees are usually regulated only in a limited way, if at all.

HARTFORD ''THE Nuremberg Trials,'' Donald J. Long remarked to a companion last Wednesday as he walked into the State Senate chamber where the television cameras and a witness table were being set up for the start of hearings in an investigation of why the Connecticut State Police did not assist local police at a rally by the Ku Klux Klan at Meriden on March 21. Mr. Long, the state's Public Safety Commissioner, and a contingent of State Police officials sat waiting as the General Assembly's Public Safety Committee began its laborious hearing. But the committee adjourned after three hours, mostly spent watching a State Police videotape of the Klan rally and the subsequent violence, and Mr. Long was told he would have to wait until Friday, when he was scheduled to finally give his version of what happened at Meriden. Mr. Long said he was ''very disappointed'' at not being able to testify at the outset of the hearings. ''You seem annoyed,'' a reporter remarked. ''Yes, I am,'' the Commissioner replied.Whatever the outcome of the investigation, Donald Joseph Long has become the man in the middle in a multi-sided dispute involving state troopers and their leader, the state and local police forces, the Governor and state legislators.

set with 3 line initial and ruled byline By MURRAY CHASS What, Gene Michael was asked the other day, was he going to do as the new manager of the Yankees to improve on the 103 victories engineered by Dick Howser, the most recent old manager, last year? ''I don't know that you have to improve on last year,'' the Yankees' second successive rookie manager, responded. ''You might have to win less.'' Michael meant it might take fewer victories to win the American League's Eastern Division championship. But to please the boss, Michael will have to win more - more than the division championship.

-------------------------------------------------------------------- SUSAN HELLER ANDERSON writes frequently from England. By SUSAN HELLER ANDERSON In British polo circles the rumor circulates that the main reason The Wedding has been scheduled for Wednesday, July 29, is because Prince Charles hopes to play in the Imperial International Polo event the previous Sunday. Maj. Ronald Ferguson, deputy chairman of the Guards Polo Club at Windsor and the Prince's polo coach, prefers not to comment on the wedding date, but does say, ''He really loves his polo.'' The game, which has been compared to playing golf from a lowflying helicopter, inspires fanatical devotion from both players and fans. It combines the speed and glamor of horse racing, the concentration of tennis, the dangers of skiing, the precision of golf and the violence of hockey. ''I love the game, I love the exercise,'' the Prince was quoted as saying in a recent biography. ''It's my one extravagance.''