What was going on when I was born?

THE decision to buy an old or historic house used to be the beginning of a sentimental, rather than practical, odyssey. Buyers went ahead, regardless of the potential maintenance headaches, because they were captivated by the house's charm and by legends of generations past that seemed to permeate every creaky stair and beam. They did not expect any help with their problems, nor did they expect to have anyone tell them what they could or could not do to the house. Today, however, the purchase of such a house is becoming more and more like taking in trust a little bit of the national treasure. The house is now likely to be in an historic district, and buyers should be aware that such a designation is not simply honorific. It comes with legally binding restrictions and responsibilities in addition to very tangible benefits rarely available to owners of these properties before.

Chad ChallengePuts the FrenchIn a Testy MoodDispatching French troops to prop up a former African colony was bound to be awkward for Fran,cois Mitterrand, a Socialist President who had castigated his predecessors for doing just that. So last week, as several thousand French paratroops flew into Chad and the neighboring Central African Republic, Mr. Mitterrand loudly changed the subject. He authorized the newspaper Le Monde to portray him as staunchly resisting purported pressure from Washington. Mr. Mitterrand was acting only to rescue Africans from heavy-handed American tactics that threatened to create a dangerous new East-West battlefront, the paper said. President Reagan had sent so many messages, added Le Monde, that Mr. Mitterrand hadn't bothered to answer them all.

LUGANO, Switzerland The most spectacular exhibition in Europe this summer is not in Paris or London or Berlin but in a villa on the eastern tip of Lugano, Switzerland. In exchange for a loan of 40 paintings from his celebrated Old Master collection, Baron Hans Heinrich Thyssen-Bornemisza has borrowed 40 late 19th- and early 20th-century French paintings of the highest quality from the Hermitage Museum in Leningrad and the Pushkin Museum in Moscow. The show is of particular interest, since the paintings have been rarely seen in the West since they were acquired by the two great Russian collectors, Ivan Morozov and Sergei Shchukin, in the years prior to World War I. This Impressionism to Cubism greatest-hits shows, installed in the private quarters of the baron's Villa Favorita, the building that houses his Old Master museum, continues through Oct. 15. The Soviet authorities' selection of the baron's top 40, which includes paintings by Rogier van der Weyden, Titian, El Greco and Goya, will be on display at the Pushkin from Sept. 12 to Nov. 14 and the Hermitage from Nov. 19 to Feb. 1, 1984.

Chad ChallengePuts the FrenchIn a Testy MoodDispatching French troops to prop up a former African colony was bound to be awkward for Francois Mitterrand, a Socialist President who had castigated his predecessors for doing just that. So last week, as several thousand French paratroops flew into Chad and the neighboring Central African Republic, Mr. Mitterrand loudly changed the subject. He authorized the newspaper Le Monde to portray him as staunchly resisting purported pressure from Washington. Mr. Mitterrand was acting only to rescue Africans from heavy-handed American tactics that threatened to create a dangerous new East-West battlefront, the paper said. President Reagan had sent so many messages, added Le Monde, that Mr. Mitterrand hadn't bothered to answer them all.

There were cheers again at Giants Stadium tonight for Lawrence Taylor, boos for Scott Brunner and Phil Simms, and then Jeff Rutledge further confused the Giants' quarterback situation with a fine fourth-quarter performance as the Giants defeated the Baltimore Colts, 27-14, in an exhibition game. ''I'm not going to have an answer tonight,'' said Bill Parcells, the undefeated head coach. He raised his winning streak to three but still is not sure who will be his starting quarterback when the National Football League regular season opens in two weeks. Parcells was also not sure who his place-kicker would be after Joe Danelo kicked himself back into contention by hitting field goals of 42 and 40 yards into gusty, swirling winds. Meanwhile, Ali Haji-Sheikh, the rookie who had apparently taken the lead for the job with five field goals a week ago, missed his only attempt, a 36-yarder.

Wall Street Guessing Game Divining what credit course the Federal Open Market Committee will chart at its next meeting is a popular Wall Street ritual. The policy-making arm of the Federal Reserve convenes in Washington on Tuesday, as it does every six weeks. And the message analysts read in their crystal balls is that Fed policy - and hence interest rates - will remain unchanged. In May the panel decided to tighten the availability of credit for the first time this year, and that sparked higher rates. There has been further tightening since then, but with money supply growth slowed for the past two weeks, the inflation incentive to tighten again should be lessened.