What was going on when I was born?

The Seventh Regiment Armory on Park Avenue will be turned into a do- it-yourselfer's paradise Friday when the second annual Big Apple Fix-Up opens for a three-day run. More than 150 exhibitors will display and demonstrate products for renovating, remodeling and repairing houses and apartments.

MADISON AVENUE, which once was to advertising what Broadway is to show business and Central Park West to psychoanalysis, is no longer the same. The ad men are going and the bankers are coming. Not just coming, in fact - they are already there. In less than four years, more than two dozen banks from all over the world and this country have opened offices on Madison Avenue between 42d and 57th Streets. According to Andrew Roos, a vice president of Williams Real Estate Company, there are more than 50 banking offices within two blocks of the corner of Madison and 55th Street. The immediate reason for this particular surge of midtown money-changing, real-estate specialists and bankers say, is a lack of attractively priced space on Park Avenue. But a more fundamental explanation is the considerable increase in financial activity in New York City since the creation here two years ago of a free-trade zone in international banking.

HE is a big man with a full beard who might look intimidating if it weren't for the smile on his face and his gentle nature. He once played for the Los Angeles Rams and was part of a defensive line that was called the Fearsome Foursome. But now, Merlin Olsen can be seen on television extolling the virtue of flowers. In the past five years, Olsen estimated that he has turned down 10 major advertising campaigns and ''big dollars'' waiting for one that he felt was suited to his nature and tastes. ''What I like about this one,'' Olsen said, of the new Florists' Transworld Delivery Association (FTD) ads, ''is that in only one of the commercials is there any reference to me as a football player. And what I also like is that the commercial shows you don't have to be a softie to give or receive flowers. Too often, the people in advertising are not creative enough to get away from stereotypes.'' In recent years, television commercials have afforded a number of athletes the opportunity to move gracefully from the playing field to an alternative career. The money boom in professional sports and the growing awareness of physical fitness have been credited by those in advertising with giving many athletes the kind of visibility that only a few had enjoyed previously and which had been primarily associated with Hollywood stars.

The most conspicuous and, for the moment, most emotional political conflict being waged in South Africa is not the fundamental, gradually sharpening struggle between white nationalists and black nationalists. It is white versus white. More specifically, it is Afrikaner versus Afrikaner. The cleavage in the dominant white group - no more than 2.8 million people who are scarcely 8 percent of the 32 million people inside the country's traditional borders - results from a bold attempt by Prime Minister P. W. Botha to broaden its political base. His new constitution, which has been adopted by the white Parliament and is awaiting approval by the white electorate in a referendum on Nov. 2, seeks to do this by extending limited political rights to brown, but not black, South Africans.

Columbus House, a slim 18- story condominium apartment building nearing completion on the west side of Columbus Avenue between 78th and 79th Streets, looms over its low-rise neighbors, but it makes a design gesture to the American Musuem of Natural History, the massive landmark complex sitting just across the avenue. A search was made for a curtain-wall brick that would closely resemble in tone and texture the museum's rough- cut limestone facade.

PHILADELPHIA For nearly half a century, the Philadelphia Orchestra has been known as much for its sound as for its music. The word ''Philadelphia'' connoted a string texture at once soft, rich and powerful. It was an unmatched quality, one cultivated during Leopold Stokowski's many years with the orchestra and then pruned, enriched and perfected by Eugene Ormandy who took over the Philadelphia in 1936 and did not leave until he became conductor laureate in 1980. This beautiful quality lay often like a great oppressive weight over the vast repertory of music Mr. Ormandy seemed happy to apply it to. One orchestra violinist, recalling his first rehearsal under Mr. Ormandy many years ago, remembers the pressure on the bows all around him: ''I actually couldn't hear myself play.'' ''From Mozart to Sibelius,'' remembers another, ''it all tended to be the same.'' Riccardo Muti, who brings the Philadelphia Orchestra to Carnegie Hall on Tuesday, is entering his fourth season as heir to this grandly luxuriant, but obstinately uniform, way of making music; and, as the orchestra's music director, Mr. Muti's task has been to create many styles where previously there was one. ''There is no 'Philadelphia sound,' '' he says in his quiet, laconic way. ''There is a Mozart sound, a Brahms sound, a Mahler sound.''

In the process of working on the tribute, Mr. Martins found himself challenged by television in much the same way as his distinguished predecessor. ''Ballet on television is always a compromise between that medium and the dance,'' Mr. Martin said recently, sitting in his office backstage at the New York State Theater. Balanchine himself had long wanted to film ''Vienna Waltzes'' a sumptuous evocation of the Viennese waltz created by the choreographer in 1977. ''He talked with John and Emile about the possibility of doing it,'' Barbara Horgan, Balanchine's assistant and his executor, said. ''But it would have cost $10 million to do it in a studio, and no one was about to spend that.'' In November, Mr. Goberman approached Miss Horgan with the idea of taping a City Ballet special. ''George was in the hospital,'' Miss Horgan recalled. ''But I said I'd talk to him and see if he had some wise remarks.''

THERE is a story Clayton Akin likes to tell about two kindergarten students playing outside during recess. Seeing a 747 jet airliner flying overhead, they get into a discussion about its technical capabilities. In the middle of their conversation, the school bell rings, and one of them remarks to the other, ''Well, I guess it's time to go back in and string those darn beads again!'' ''Youngsters are better prepared for learning today,'' said Dr. Akin, superintendent of the Rye Neck Union Free School District. ''And they're ready now to have a kindergarten program that will match their needs.'' And so, in 1979, Rye Neck instituted what Dr. Akin described as ''an idea whose time has come,'' an all-day kindergarten that replaced the more traditional half-day sessions. ''It met the needs of parents, and it met our instructional needs,'' he explained. ''Children are ready to come to school earlier now than at any other time.''

New York State health officials have told Mount Sinai Medical Center that they will not consider approving the hospital's rebuilding plan unless it agrees to help rescue North General Hospital, a small, private institution struggling to survive in Harlem. The same condition was set by the New York City Health Systems Agency, a federally financed health planning body that has the power to deny new hospital construction. Health officials said this was the first time such a condition had been placed on an approval of a hospital's rebuilding plan in New York State. Both the state and the agency believe that small community hospitals, such as North General, can no longer make it on their own in New York, but that they are nevertheless essential to the health of the impoverished communities most of them serve.

There's life in the old champ, after all. Penn State, 1982 national collegiate football champions but loser of its first three games this season and an 8-point underdog before a record crowd of 85,614 in its own stadium, rose up today and knocked third- ranked Alabama from the unbeaten ranks with a 34-28 victory. The old champ had to survive a final-round knockdown. A game in which there were 1,091 yards of offense ended with Penn State stopping an Alabama run from the Nittany Lions' 2-yard line for no gain as the Crimson Tide, trailing, 34-7, entering the fourth quarter, mounted a magnificent comeback led by their quarterback and Heisman Trophy candidate, Walter Lewis.

FOR many Wall Street forecasters, the big question these days is whether interest rates will tumble a point by Thanksgiving, or two by Christmas. Such predictions may be critical to the bond market and may fascinate forecasters, but they hide a deeper truth that in recent months has come to dominate the thinking of an increasing number of economists here and abroad. For the United States economy - the linchpin of the industrial world - has entered a new era this year: one of high interest rates. No matter what rates are viewed - whether on bonds or bills, Treasuries or corporates, Triple A's or junk bonds - they are higher now than they have been in recent memory and a good deal higher than most economists thought possible at this stage of a recovery. Moreover, it is clear to many analysts that high rates are going to be with us - and, therefore, with much of the rest of the world - for a very long time. The 5 percent prime, it seems, has gone the way of the 4 percent unemployment rate.

FRANK DE BENEDETTO lived with the same foster family in Baldwin for most of his 20 years - since he was 17 months old. ''The social worker always pushed adoption,'' he said, ''but I always felt like I was born to this family. I wouldn't feel any different if I was adopted.'' Because a child 14 years old or over cannot be adopted without his consent, the idea was not pursued once he had reached that age. Out of nearly 1,000 children in foster care in Nassau County, some 250 are teen-agers or young adults like Mr. De Benedetto who do not expect to be adopted. Since they will eventually ''age out'' of the foster care system, their foster care agencies are required by the New York State Child Welfare Reform Act to help them develop a plan for independent living. Foster care ends when a child reaches the age of 18, or 21 for someone who is still in school or a training program.