What was going on when I was born?

The hoopla of September that once ushered in the new model year here is long gone. Trying to make the best of a market that has stubbornly refused to respond to three years of rebates, new models and advertising blitzes, car makers have stretched the season for introducing new cars to the point where it is now as long as a Detroit winter. While this September will bring some new offerings, it will be marked more by marketing wrinkles and luxury models rather than breakthroughs, and the introductions will continue through the spring of 1983. One of the few new developments will be the appearance of another domestic auto manufacturer on Nov. 1, when the Honda Motor Company plans to start production of its 1983 four-door Accord models in Marysville, Ohio.

Israel complained today that Palestinian guerrillas leaving Beirut were being allowed to violate a carefully negotiated withdrawal plan through improper supervision. Officials in Jerusalem said there was no apparent registration of the guerrillas, that they were departing with weapons and equipment they should be leaving behind and that women and children disguised as men were included among those going. At the same time, the Israelis expressed satisfaction at the election of Bashir Gemayel as President of Lebanon. Prime Minister Menachem Begin sent Mr. Gemayel, the leader of the rightist Christian militia that has been long allied to Israel, a message signed ''Your friend Menachem Begin.''

''Leisure should be relaxing. Possibly you like complicated puzzles, or chess, or other demanding intellectual games.

The Department of Justice and the Pentagon have created a special investigative unit to prosecute fraud in the Government's multibillion-dollar purchases of military equipment and services, according to Defense Department officials. Michael Eberhardt, director of the Defense Department's Criminal Investigations, Policy and Oversight Office, said that the unit was intended to ''fill a sorely needed vacuum of support from the Justice Department for Defense Department's criminal investigations.'' The new group, which met informally at the Pentagon for the first time Friday, is being organized in part to ease public concern that the $178 billion that the Reagan Administration has requested for the military in the next fiscal year might be misspent. Administration officials also hope that the creation of a high priority unit to combat fraud will ease some of the political criticism of the large increases in military spending being sought at a time when social expenditures are being slashed.

EDWARDS AIR FORCE BASE, Calif. ASOUND from yesteryear is being heard again in the skies over the Dryden Flight Research Facility here. It is the sound of propellers, for aeronautical engineers, in their efforts to develop more fuelefficient airplanes, have been busy of late reinventing the propeller. Flight tests, scheduled to end next week, have encouraged the National Aeronautics and Space Administration to negotiate a contract for new propeller construction, and helped persuade Congress to approve funds for further research that is expected to lead to propdriven airliners capable of flying as high and as fast and presumably as quietly as today's jets. By its action, Congress overturned the Reagan Administration's plan to kill NASA's propeller research program. G. Keith Sievers, manager of the Advanced Propeller Project at NASA's Lewis Research Center in Cleveland, said current studies have found that 150-passenger airplanes powered by a couple of advanced turboprop, or propfan, engines would burn one-quarter less fuel than the most efficient jets. Such estimates appeal to airplane manufacturers and the financially-troubled airline industry, where rising fuel costs now account for as much as 60 percent of direct operating expenses.

The stock market extended its strongest rally on record yesterday as the Dow Jones industrial average rose to an eight-month high. Trading volume on the New York Stock Exchange, fed by heavy buying by pension funds and other cash-rich institutions, surpassed the 100-million-share mark for only the second time. ''What you saw was pure panic buying,'' declared William G. Garrison, president of Garrison, Keogh & Company, an investment advisory firm. ''Institutions are telling their money managers to commit funds to this runaway market.''

They grace the tennis courts of Wimbledon, the golf courses of Palm Springs and the wings of the sleek Harrier II fighter planes. Despite such good company and krypton-like properties - stronger than steel, lighter than aluminum -graphite or carbon fibers, which look like strands of black yarn, have yet to make much money for the chemical industry. Industry executives believe, however, that they have solved the problems of high costs and special design that stymied the development of carbon fibers in the past, and they expect demand to rise to 3.5 million pounds a year by 1984, from 1.2 million pounds last year. Some analysts believe that the market could grow to 10 million pounds by the end of the decade. About two-thirds of the demand will come from the aerospace industry, they say, with the remainder divided between sporting goods and industrial uses.

Federal Judge Harold H. Greene, apparently clearing the way for a final settlement of the eight-year-old antitrust suit against the American Telephone and Telegraph Company, today rejected a Justice Department request that he limit the ability of Bell's 22 local telephone companies to sell switchboards and other telephone equipment after they are split off from the parent. The proposed restrictions, Judge Greene wrote in a five-page memorandum today, ''would not be in the public interest.'' The divested operating companies would be relatively small corporations with fewer opportunities for anticompetitive behavior than have been available to the Bell System, he noted, and would pose little threat to other equipment manufacturers.

MANDEE and Stacee Rasner, who are 6 and 10 years old respectively, live on a 7,040-acre cattle ranch outside Yoder, Colo. They like to travel to neighboring states to watch their father, Roger, perform in rodeos. They can do this easily because their school is closed on Fridays. Edison School District 54 is one of a growing number of districts, all of them small and rural and most of them in Western states, that are moving to four-day weeks. The original motivation was economic - to save on transportation and heating bills - but school officials say the four-day week has educational benefits as well, and parents and students seem to like many of its other effects. Joseph Newlin, director of the Office for Rural Education at Colorado State University, estimates that about 100 school districts in the United States now follow the plan, with the number growing each year. ''Judging by the inquiries we are getting,'' he said, ''I think it's going to be a national trend,''

International The new President of Lebanon will be Bashir Gemayel, the leader of the rightist Christian militia. Residents of Christain-dominated east Beirut were jubilant. But in predominately Moslem west Beirut, the houses of three members of Parliament who took part in the electoral session were blown up. (Page A1, Column 6.) Arab and Palestinian officials in Damascus believe that the election of Bashir Gemayel as Lebanon's new President is likely to touch off new strife. Any new fighting between Moslems and Christians, it was said, would make it more difficult to withdraw Syrian and Israeli forces. (A1:5.)

Americans who invested in Mexican financial instruments, attracted by high interest rates and by the transactions' confidentiality, have lost hundreds of millions of dollars as a result of this country's acute financial crisis, according to local investment analysts. The loss stems from the Government's decision last week that foreign currency investments would be convertible only to pesos, and at an unfavorable exchange rate - the so-called Mexdollar rate. That rate was set at 69.50 pesos to the dollar, while the dollar traded today at between 95 and 100 pesos. The multitier system was introduced after a new flight of capital forced the Government to impose partial exchange controls for the first time in its history.

Bashir Gemayel, the leader of the rightist Christian militia, was elected President of Lebanon today. East Beirut, the stronghold of Maronite Catholics, exploded in an ecstasy of gunfire this afternoon as Christian militiamen drove through the streets with portraits of their leader taped to windshields, rifles blazing away into the air. In predominantly Moslem west Beirut, the houses of three legislators who had participated in the special session of Parliament at which Mr. Gemayel was elected were blown up. Among them was that of the Speaker, Kamal Assad.