What was going on when I was born?

President Reagan, urging legislators to ''seize this historic moment'' and overhaul the nation's tax system, said today that he would introduce a plan on tax revision to Congress next month. ''It's time for change, sweeping change,'' said Mr. Reagan. ''And when we return from the economic summit in May, we intend to move.'' Mr. Reagan said Treasury Secretary James A. Baker 3d expected ''to advance a proposal that can win bipartisan approval this year.'' In response, Democrats said that the President's tax revision of 1981 was responsible for increasing tax advantages for the well-to-do.

Last weekend and this, New York audiences have been lining up at the Museum of Modern Art to see Edgar Reitz's massive, beautifully realized new German film, ''Heimat,'' which, in a running time of almost 16 hours, chronicles in minute detail the life and times of one small Rhineland village from 1919 to 1982. The film, financed mostly by television interests, has been shown both on television and in theaters in Germany. It's virtually certain to receive some sort of theatrical release in this country before going to television, thus following the pattern set by the 1983 American release of Rainer Werner Fassbinder's masterly, 15 1/2-hour adaptation of Alfred Doblin's ''Berlin Alexanderplatz.'' Ten days ago, a lot of television viewers sat through ''A.D.,'' the sometimes riotously solemn, five- part, 10-hour, post-Crucifixion biblical epic, conceived and written by Vincenzo Labella and Anthony Burgess as a sequel to their 1977 collaboration, ''Jesus of Nazareth,'' directed by Franco Zeffirelli.

In 1979, the Port Authority of New York and New Jersey bought from Conrail a 90-acre tract in Elizabeth, N.J., near Newark International Airport with plans to establish an industrial park that would help the area's economy. Now, after a five-year delay - caused, in part, by a toxic-waste clean-up of part of the site - the agency will grant the first development land lease for the Elizabeth Industrial Center.

BUSINESS expansions used to mean good times for corporate chief executives. But this recovery has brought with it a heavy dose of corporate stress. The creaking financial system, surging imports and shrinking profit margins have wrought misery on whole industries. And for specific companies in those industries, the hostile and unpredictable takeover wars of the last two years have raised corporate insecurity to new heights. Few companies, it seems, are immune to the combat. Flaring first in the oil patch, the hostilities have spread to the communications, drug, forest products and rubber industries. Chiefs of the target companies have had to divert their attention from running their corporate ships, instead devoting their time to plotting strategies to keep the company ''out of play,'' or fighting the battle if those strategies did not work. The diversions have been so widespread that Andrew C. Sigler, chairman of Champion International and head of a Business Roundtable task force on hostile takeovers, warned recently that ''these pressures can undermine the long-term strength of our economic system.''

Top officials from the Soviet Union and the United States today accused the other side of impeding the arms-control talks in Geneva. Kenneth L. Adelman, head of the United States Arms Control and Disarmanment Agency, contended that the Soviet Union's recent public statements on arms control threatened progress by breaching the confidentiality of the negotiations. The Soviet Ambassador to the United States, Anatoly F. Dobrynin, who appeared with Mr. Adelman at a weeklong conference at Emory University's Carter Center on international arms control issues, contended that refusal by the United States to disclose details of its space-based missile defense program was slowing the talks. Early Deadlock Predicted Although neither Mr. Adelman nor Mr. Dobrynin would comment directly on the progress of the talks, experts gathered here said the talks appeared headed for an early deadlock.

The Mets, the team of improbable encores, supplied another one yesterday when they won for the fourth straight time by the margin of one run: a ninth-inning home run by Darryl Strawberry that defeated the Cincinnati Reds, 2-1. Not only that, but Strawberry made a winning pitcher of an improbable hero: Roger McDowell, the 24-year- old rookie from Cincinnati who underwent elbow surgery early last year and pitched only seven innings in the Texas League. With his sinking fastball and remarkable control, the rookie made the Mets in spring training. Now, he has pitched three innings in relief in his first two appearances in the big leagues, and has won two games.

The new leader of the Sudan said today that the military would rule the country for probably no more than one year, during which a painful economic austerity program would be kept in place. The leader, Gen. Abdel Rahman Siwar el-Dahab, also said the Islamic law imposed by former President Gaafar el-Nimeiry in October 1983 would have to be ''amended'' and ''modified'' to eliminate ''incorrect and excessive'' punishments inflicted by Mr. Nimeiry's courts. The general made these and other remarks in a 45-minute interview, his first with Western reporters since the army toppled the nearly 16-year-old Nimeiry regime in a bloodless coup. He categorically denied that the reason senior officers seized control of the Government last Saturday, overthrowing President Nimeiry, was to pre- empt a coup by junior officers amid widespread popular unrest. 'Absolutely Not True' ''This is absolutely not true,'' the general said. ''We had been observing the situation since it started a week earlier, and it became quite clear to us that unless we intervened at the right moment, this would lead to bloodshed and it would destroy the unity of this country.''

There is perhaps no more telling symbol of the transformation of the Cobble Hill section of Brooklyn than the current effort to convert the 63-year-old Sacred Heart and St. Stephen's School on Hicks Street into condominium apartments. In recent years the neighborhood of turn-of-the-century brownstones and tree-lined streets, with its vital shopping district, has been a magnet for single professionals and young married couples. Moreover, its largely Italian and Roman Catholic population has been diluted over the years as its ethnic mix has broadened. A dwindling enrollment prompted the Roman Catholic Diocese of Brooklyn to close the 4 1/2- story school last June and sell it. The buyers, Blundon Thylan Associates Inc., a real-estate company, and Bernard Ettinger, are converting the school into 34 one- , two- and three-bedroom units.

Astronauts today released a second communications satellite from the space shuttle Discovery's cargo bay, but a mysterious failure left the satellite powerless and unable to take off on its own to reach its intended higher orbit. Teams of engineers were studying the possibility of returning the shuttle to the disabled satellite for a close-up inspection and perhaps a space walk by astronauts to restore life to the dormant craft. The inspection could come Monday and the space walk on Tuesday. Satellite Fuel Poses Danger Such an operation, never before attempted, would not be without risk, since the satellite, Leasat 3, is fully fueled and its rocket primed for ignition.

Ray Floyd, who has a secret game plan on how he should attack Augusta National Golf Club, said he followed that blueprint to move into the lead by one shot after three rounds of the 49th Masters. An eagle 3 on the par-5 13th hole did not hurt, either. Floyd, the 1976 Masters champion, came from three shots off the second- round pace and scored three-under- par 69 today for a 54-hole total of 212. And, in one of the strongest comebacks in any major tournament in history, Curtis Strange moved up to second at 213 after scoring 68. Strange, the 30-year-old who leads this year's PGA Tour money list, did not expect to be playing by now after shooting an eight-over 80 in Thursday's first round.

Secretary of State George P. Shultz and Foreign Minister Shintaro Abe of Japan met today to continue efforts to avoid a trade war between their countries. ''We are all threatened by protectionism,'' Mr. Shultz said with Mr. Abe standing and nodding by his side in the State Department lobby after a two- hour session. ''Protectionism is not a cure for an illness,'' Mr. Shultz added. ''It is itself an illness and one that can spread like a plague.''

IT is a ''wild and woolly'' tract, inhabited by coyotes, wild turkeys, beavers and ''an occasional bear or bobcat,'' said Randi S. Lemmon of the Housatonic Valley Association, a conservation group based in Kent. Though most people might not associate such an unspoiled wilderness area with Connecticut, he said, the land, some 1,800 acres, is in lower Litchfield County, in the towns of Kent, Cornwall and Sharon. And under an agreement just reached between the National Park Service and the Stanley Works, the New Britain-based tool company, the river valley property will be permanently protected and its use restricted to recreation and agriculture. The Federal Government has paid Stanley Works $3,131,300 for the land to assure permanent protection of some five miles of the Appalachian Trail, which runs along the west bank of the Housatonic River. The transaction included the purchase of 1,281 acres on the west side of the river and the acquisition in conservation easements of 504 acres on the east bank, which is between the river and Route 7. Most of the property is in Kent, with about 400 acres in Sharon and 100 in Cornwall.