What was going on when I was born?

Two and a half years after the nation's worst nuclear accident, at the Three Mile Island nuclear plant in Pennsylvania, the Nuclear Regulatory Commission, which oversees the industry, is undergoing a profound change. The five-member commission, according to industry representatives, legislators and opponents of nuclear power, is seeking to transform itself from a somewhat troubled and passive monitor of nuclear power into a tough-minded regulator of quality and safety. The shift, which began slowly after the accident at Three Mile Island in March 1979, is now being promoted by Nunzio J. Palladino, the commission's new chairman. In six months on the job, Mr. Palladino has startled proponents and opponents of nuclear power alike with a series of frank assessments of weaknesses and failings in nuclear plants, the agency's inquiries and the international nuclear safeguards system. ''The N.R.C. will not cave in to pressures from the utilities,'' Mr. Palladino told a Congressional subcommittee today. Acknowledging that agency investigations have sometimes not been sufficiently aggressive, he added: ''I am aware that we have a problem and we will address it.''

Rory F. McFarland, founder and president of Advanced Energy Technology Inc., is an easy target for skeptics. His company's unconventional gear design, called the Anti-Friction Drive, was developed in Boulder, Colo., far from the nation's industrial heartland, without help from any mechanical engineer trained in gear technology. The components of this new device move in ways that are almost impossible to track without a computer. There is no independent evidence that it is as efficient as Mr. McFarland contends or that it can be manufactured at a reasonable cost. Besides, there is the mediocre track record of his company's earlier designs. And, of course, there is his resume. The 29-year-old entrepreneur freely acknowledges that he is a college dropout whose business experience before his plunge into reinventing the gear consisted of ''light-duty entrepreneurship'' - part ownership of a now-defunct rare coin shop in Denver and of an equipment-leasing business and home and apartment renovation in Boulder.

The Dow Jones industrial average plunged 15.03 points, to 871.48, amid heightened tensions in Poland and the Middle East. It was the index's biggest drop in 14 weeks. Declining issues outstripped gainers by 1,373 to 243 on the Big Board as volume eased. (Page D1.) Bond prices rebounded sharply yesterday, with long-term government issues gaining as much as two full points. Late in the day, however, the Treasury auctioned six-month bills at a rate of 11.595 percent, up from 10.772 percent last week. (D14.)

FOUR years ago, a tumult of shouted slogans and waving placards shattered the dignity of the National Academy of Sciences' auditorium in Washington. The protesters were denouncing potential harm to human health and individual freedom from something mysterious called genetic engineering. The scene was a public forum held by the Academy on a new field of biological research that had suddenly exploded into public consciousness. Known to scientists as recombinant DNA technology, and to a wider public as gene-splicing, the field implied new drugs, new knowledge, new hazards and eventually, perhaps, the deliberate introduction of new genetic traits into living cells - genetic engineering. Just a few weeks ago in the same auditorium, with no placards or even raised voices, members of the National Academy of Engineering heard reports on the current state of the art of genetic engineering, and the description of techniques that had only been prophesied in 1977. ''The age of genetic engineering as applied to therapeutic proteins is here right now,'' said Dr. Michael Ross of Genentech Inc., a California company that was then only a year old and virtually unknown. Today it is well known to scientists, drug companies, stockbrokers and everyone else interested in gene-splicing research and development.

The Baldwin-United Corporation, a diversified financial services company with a growing insurance business, yesterday announced an agreement to merge with the MGIC Investment Corporation, the largest independent seller of residential mortgage insurance. The acquisition, which will cost Baldwin-United $1.2 billion, is the biggest in a series of more than 30 since the late 1960's that have turned Baldwin from a piano and organ manufacturer into a concern chiefly involved in the sale of life and casualty insurance. MGIC has about 35 percent of the market for residential mortgage insurance, which is designed to protect the lender from default. Cincinnati-based Baldwin-United will pay MGIC stockholders $52 a share. The stock has been trading in the low 40's for several months and closed at 47 3/4 yesterday, up 4 1/8 from Friday's close. Baldwin-United closed yesterday at 55 7/8, down 7/8. Both issues trade on the New York Stock Exchange.

Police officers manned bridges and tunnels around New York City early today and launched a wide and systematic 48-hour search for seven unmarked city and Federal police cars that the police said had been stolen here under unusual circumstances. The thefts of five city police cars and two vehicles of the Federal Bureau of Investigation all occurred near police facilities in various parts of the city between last February and November None had previously been made public. ''It is an unusual situation to have this many vehicles stolen without a trace of them being found,'' said Alice T. McGillion, the deputy police commissioner for public information. Thieves usually steal no more than one or two police cars a year, and these are nearly always found, she said.

Crackdown in Poland Polish workers mounted strikes throughout the country in defiance of martial law as military leaders tightened their hold. Clandestine information services of Solidarity reported strikes and worker resistance in factories, shipyards, steel mills, coal mines and even academic institutions in Warsaw and all other major cities and regions. Lech Walesa, Solidarity's leader, who was technically not detained by police was said by Government officials to be in a Goverment rest house.(Page A1, Column 6.) No widespread unrest in Poland has been indicated by diplomatic and intelligence reports reaching the United States, according to senior American officials. The reports were spotty because of an internal communications blackout in Poland. (A18:1-2.)

Murray L. Weidenbaum, President Reagan's chief economic adviser, today defended the prospect of sizable budget deficits, saying a balanced budget was not ''one of the fundamentals'' of the Reagan economic program. Mr. Weidenbaum said that the new budget the President is scheduled to send Congress early next year would show a deficit for the fiscal year 1982 of less than $100 billion and smaller deficits for the fiscal year 1983, which starts next Oct. 1, and for the fiscal year 1984. A recent internal working estimate projected the 1982 deficit at $109 billion. As for the balanced budget in 1984 that Mr. Reagan first promised during the 1980 election campaign, Mr. Weidenbaum cited the President's Budget Message of last February and said ''that was not presented as one of the fundamentals of the program.''

The first official Soviet comment on events in Poland said today that they were ''an internal matter.'' It described any ''different interpretation'' implying Soviet manipulation as an attempt in itself to interfere in Polish affairs. The statement, issued by the Government's press agency Tass, indicated that the Kremlin, was eager to counter charges in the West that Soviet pressure had forced the Polish authorities to impose martial law and suspend the operations of the Solidarity trade union, and the statement did not explicitly endorse the crackdown. Moves Termed Polish Initiative The Soviet press has presented the crackdown as a purely Polish initiative to save the country from the ''mortal danger'' of counterrevolution.

WHEN Bernard Harleston walks about the Harlem campus of City College, he takes special note of the massive, laterally jutting lines of the campus's nearly completed North Academic Center with its high marble-clad foundation thrusting outward like the prow of a great ship into Amsterdam Avenue at West 138th Street. He then looks across Convent Avenue, barely 100 yards away to the stark contrast of the neo-Gothic verticality, cloistered ambiance and richly textured surfaces of Shepherd Hall, built in 1910 and long a college symbol as the site of everything from registration to demonstrations. ''They are symbolic of change on the one hand and continuity on the other,'' mused Dr. Harleston of the two architectural styles that grace the 35-acre campus, which stretches from West 131st Street to West 140th Street, from Amsterdam Avenue to St. Nicholas Terrace. ''Those are the two themes I've been working with here.''

There are issues that continue to divide this nation, and the plastic Christmas tree is one of them. As Wanda Bryant stood at the checkout counter of a Christmas-tree store here the other day, she noticed a woman with a natural blue spruce and was compelled to speak out on the issue. ''That's a lovely tree,'' she said, ''but how can you stand having it in your house with all the needles and the mess all over?'' ''I certainly wouldn't have a fake one in my house,'' the woman with the blue spruce shot back. ''They're awful.'' With that, Mrs. Bryant picked up a large cardboard box containing her polypropylene ''Natural Mountain King'' Quick-A-Tree model AT 84-355-90, and stalked out.

The contested Golan Heights formally became part of Israel today as Prime Minister Menachem Begin pushed a measure through Parliament to annex the strategic zone along the Syrian border. Officials said the new measure provided that ''the law, jurisdiction and administration of the state shall apply to the Golan Heights.'' The area had been held under military occupation since Israel captured it from Syria in the 1967 war. Vote Is 63 to 21 The legislation, enacted in Parliament by a vote of 63 to 21, brings about the first change in Israel's frontiers since 1967, when East Jerusalem,and an adjoining part of the West Bank were annexed. The rest of the Israeli-occupied West Bank, Gaza Strip and Sinai have not been annexed, but remain under military government, which implies temporary Israeli control.