What was going on when I was born?

The United States warned Libya that there could be ''serious consequences'' if it interfered with the two Awacs surveillance planes that were sent to help deter Libyan air attacks on the Sudan, according to a Reagan Administration official. The Awacs were sent to Egypt to join Egyptian fighters in patrolling Sudanese airspace. (Page A1, Column 6.) Summit talks on the Common Market ran into problems when Prime Minister Margaret Thatcher of Britain again demanded far-reaching changes in the way the 10-nation European Economic Community works. A two-day meeting of European Government leaders in Brussels is widely seen as decisive for the trade-bloc's future and for Western Europe's hopes of closer economic and political unity. (A1:5.)

It was Walter F. Mondale calling. ''Is Mrs. Kuhn there?'' he asked. ''Mrs. Kuhn on other phone,'' replied Billy Kuhn, 3 years old. He hung up. The former Vice President was laughing when he called back. ''You've got a real professional operation there, Nancy,'' he said to Billy's mother.

The United States told Libya today that there could be ''serious consequences'' if it interfered with the Awacs surveillance planes that have been sent to help deter Libyan air attacks on the Sudan, an Administration official said. The State Department and the Defense Department confirmed that two Awacs planes, along with tanker planes, had been sent to Egypt to join Egyptian fighters in patrolling Sudanese airspace. Last Friday, a TU-22 bomber, said by the United States to belong to the Libyan Air Force, dropped five bombs on Omdurman, the Sudan's second largest city, and then returned to a base in the Kufra oasis of Libya. The target of the attack apparently was the Omdurman radio station, but the bombs missed, and hit other buildings, killing five people.

In the spring of 1981, a new management team at the Cherry Webb and Touraine stores in Pawtucket, R.I., met to grapple with the first annual loss in the long history of the specialty apparel chain. The chain is one of the biggest of its kind in the Northeast. And the four executives now and then glanced out of the window toward the company's distribution center one and a half miles away in South Attleboro, Mass. Most apparel chains put their main offices and distribution center in the same building, to improve communications and logistics. But for some reason lost in its history, CWT did not.

In rites of both majesty and whimsy, John J. O'Connor yesterday took occupancy of St. Patrick's cathedral chair as the eighth Archbishop of New York. ''Ich bin ein New Yorker,'' Archbishop O'Connor said, echoing President John F. Kennedy, who used German two decades ago to tell a West Berlin crowd, ''I am a Berliner.'' The archbishop drew one of many roars of applause from the congregation of more than 3,000 in the cathedral. Speaking decisively in a crisp voice, he also vowed to join a cooperative drive to overcome social ills such as hunger and to oppose abortion, and offered compassion to those who disagree with the church's views. Yesterday's ceremony completed the two-day installation of the Archbishop, which began Sunday afternoon as a formal service of canonical possession.

From a distance, the steel mill here looks like a rusted erector set rising from a thicket of Japanese tile roofs. It was in Kamaishi, hard by the Pacific Ocean on the northeastern lip of the main island of Honshu, that the modern Japanese steel industry was born more than a century ago. And so when the Nippon Steel Corporation, which owns the mill, announced in January that the largest of its two blast furnaces would be closed, drastically reducing production, the shock was augmented by an uneasy sense of historical change. The demand for steel is far less than was anticipated not long ago, the company explained, and aggressive foreign producers are taking orders away from the domestic industry. The city's Mayor talks about diversifying the economy and attracting new industries, but so far his talk sounds mostly like wishful thinking. The townspeople, meanwhile, are distraught.

The Economy Banks raised their prime rate a half-point, to 11 1/2 percent, the highest level since January 1983 and the first change in the key rate since last August. Bankers cited the increased cost of their funds, and many said the rate may well climb further. (Page A1.) Personal income climbed 0.7 percent, but spending declined a like amount in February. The drop in consumption spending, the first in seven months, was led by auto sales, which may reflect limited inventories. For the previous month, the Commerce Department report revised upward both income and spending. (D1.)

The White House is going to battle what it sees as Congressional efforts to whittle down the President's foreign policy-making authority, Administration officials said today. The fight revolves around the House and Senate bills to renew the Export Administration Act that go soon to a House-Senate negotiating conference. The Administration, in a five-page memorandum, has singled out a dozen provisions that it opposes in the two sharply differing bills. A high-level Administration trade official, who asked to remain anonymous, said that some measures, especially those affecting United States policies toward South Africa and China, were ''veto bait.''

Since January, Elizabeth Mayo had been hearing and feeling what seemed like periodic muffled explosions deep in the ground beneath her town house at 40 Hamilton Terrace in Harlem. So, she soon discovered, had many of her neighbors along the streets that make up the Hamilton Heights Historic District. Their calls to city officials seeking an explanation finally got results. Yesterday, Mrs. Mayo and four other Harlem residents spent the morning exploring a part of their community they never expected to see: the cavernous tube now being blasted out of rock hundreds of feet below street level to form the city's third water tunnel. Donning wading boots and hard hats, they descended by elevator 500 feet down a shaft just off the Harlem River Drive, slogged through muck to examine a finished concrete section of the tunnel, 24 feet wide, and rode a train nearly two miles southward to see where a mammoth drill was punching holes in dark gray rock to prepare it for blasting - 700 feet under 144th Street and Amsterdam Avenue in Hamilton Heights.

''Ich bin ein New Yorker.''- Archbishop John J. O'Connor. (A1:2.)

Gary Hart struggled today to protect what appeared to be a narrow lead among Illinois voters, in the face of a determined effort by Walter F. Mondale to catch up. Mr. Mondale, trying to avoid a defeat in the year's first Democratic Presidential primary in a major industrial state, pushed that effort in some of the harshest verbal fighting of the campaign. But Hart strategists were counting on a strong surge toward the Rev. Jesse Jackson among black voters in Two weeks before the New York primary, Mayor Koch endorsed Walter F. Mondale. Page B11. inner-city Chicago to help the Colorado Senator stave off Mr. Mondale.

A dispatch from Pawtucket, R.I., on March 6 incorrectly described the role of the National Council of Churches in connection with a ruling by the Supreme Court that the city government had the right to own and sponsor a nativity scene at Christmastime. The council filed a brief as ''friend of the court'' supporting lower court opinions that the practice was unconstitutional.