What was going on when I was born?

With renewed resolve to overcome Canada's serious and spreading economic crisis, Prime Minister Pierre Elliott Trudeau today directed his four most prominent Cabinet Ministers to exchange portfolios. Even as the officials were sworn in to their new posts this morning, Government statisticians reported that the national unemployment rate had risen to 12.2 percent last month, the highest since the depression of nearly 50 years ago. The keystone of Mr. Trudeau's Cabinet reorganization is the turning over of the critical Finance Ministry to Marc Lalonde, an aggressive economic nationalist who as Energy Minister offended major oil companies, Canadian business interests and the United States Government with policies intended to increase Canadian equity in energy development and exploitation. Administration Lightning Rod The 5l-year-old Mr. Lalonde, a confidant and adviser to Mr. Trudeau, has replaced Allan J. MacEachen, 61, an economist trained at the University of Chicago, who has been under unrelenting pressure for the last two years as the economy went into decline. Mr. MacEachen was unabashedly relieved this morning as he was sworn in as Minister of External Affairs, a post he held before taking on the Finance post. ''The leaving of the portfolio is one of the happier events associated with it,'' said the Nova Scotian. He has been an a lightning rod for the administration, attracting the scorn of critics and providing grist for political cartoonists.

The Koch administration will have to make sharp cuts in its expenses very soon to pay for the labor contract it has tentatively agreed to with municipal unions, the executive director of the state's Financial Control Board said yesterday. ''I think it's inevitable that some kind of retrenchment action will have to be taken,'' said Comer S. Coppie, the head of the Control Board, which must certify that the city's budget is balanced. ''And the sooner they do that, keeping in mind that time is money, it will be to their advantage.'' Mr. Coppie said the necessary actions could include a hiring freeze and cutbacks in programs. He said layoffs did not seem to be necessary.

The Republican-controlled Senate today overrode President Reagan's veto of a $14.1 billion supplemental spending bill, completing the first major defeat administered to the President by the 97th Congress. The vote, 60 to 30, barely provided the two-thirds majority needed to enact the bill. The House voted on Thursday, 301 to 117, to override the veto. In the Senate, as in the Democratic-controlled House on Thursday, the vote to override signaled a breakdown of the Republican unity that had given the President an unbroken string of victories on fiscal measures. Twenty-one Republicans, most of whom were campaigning for reelection or were members of the fiscal committees, joined 39 Democrats in voting to override the veto. Four Democrats joined 26 Republicans in supporting the President.

A thief who apparently hid in the American Museum of Natural History after it closed stole 25 Mayan jade artifacts and escaped by rope from a second-floor window, authorities said yesterday. Detectives said the thief had broken into the glass display case containing the artifacts, which date from 300 to 900 A.D., and had been able to get away unseen on the street because the rope had been obscured by trees. The items were insured for $478,000, according to museum officials, but Dr. David Hurst Thomas, chairman of the museum's department of anthropology, said they were regarded as priceless and ''irreplaceable'' because they were of ''great scientific and esthetic value.'' ''These are not like gems,'' Dr. Thomas said. ''The artifacts are of value not because they are jade - there are items being made today from jade taken from the same quarries - but because they are objects of art.''

Secretary of State George P. Shultz said today that although key Arab peace proposals were ''at considerable variance'' with President Reagan's Middle East plan, there was the possibility of a ''breakthrough'' if Arab leaders had in fact decided to recognize Israel's right to exist. Mr. Shultz's fairly hopeful interpretation was the first authoritative American response to the proposals.But in Jerusalem, the Israeli Foreign Ministry rejected the plan, which was announced Thursday night in a communique issued at the end of a meeting of Arab League leaders in Fez. The Israelis said it was a design for the eventual annihilation of their country. (Pages 4 and 5.)

President Reagan responded to his defeat on a budget veto today by warning members of Congress that they would have ''a lot more chances, because I'm going to do a lot more vetoing.'' Mr. Reagan conceded his disappointment at the reversal, after 20 months of victories in Congress, but he denied that he was losing his touch. ''No, I don't think so,'' he said. ''I wasn't aiming for a scoreless game. We'll see the next time out.''

Moscow's telephone links with much of the outside world were cut off for several hours today by what officials described as an equipment failure at the Moscow international exchange. The breakdown followed severe cutbacks over the summer in the number of telephone lines between the Soviet Union and the West as well as virtual elimination of direct dialing into or out of the country. Soviet communications officials denied that today's blackout was related to the cutbacks and attributed the problem to a breakdown in automatic switching equipment at the Moscow exchange. (An official of the American Telephone & Telegraph Company said service interruption appeared to be the result of a technical breakdown. Page 3.)

Denmark's first non-Socialist Government in seven years was officially installed today amid growing rumors of a Danish devaluation.

The director of the United States Arms Control and Disarmament Agency said today that the Soviet Union wanted to bring all Europe, Asia, Africa and the Middle East under its control, leaving the United States ''no choice but to acquiesce in Soviet hegemony.'' The agency's director, Eugene V. Rostow, said that a ''wholly onesided'' Soviet proposal in current arms negotiations was aimed at achieving these goals and that Moscow might succeed unless the United States maintained a strong nuclear deterrent. He said the Soviet Union was demanding absolute security for itself, ''which is tantamount to absolute insecurity for all other countries.''

China's paramount leader, Deng Xiaoping, formally became only an adviser to the Communist Party today, but none of the other members of the top leadership joined him in the role. The announcement of 172 members of a newly created Central Advisory Commission did not include the names of Ye Jianying, who is 85 years old, or other elderly members of the Politburo's Standing Committee, which rules China. Two other lesser Politburo members, Geng Biao, 73, and Xu Shiyou, 76, joined Mr. Deng on the Central Advisory Commission, which was set up by the current 12th party congress to attract elderly officials into dignified retirement and make room for younger people. While Mr. Deng had let it be known that he might move back to what has been called the ''second line,'' the move is not expected to diminish his authority. It should relieve him from daily duties and let his proteges, Prime Minister Zhao Ziyang and Hu Yaobang, currently party Chairman, build up their respective power bases.

Over strong objections from the State Department, the Commerce Department has approved the sale of 500 electric-shock batons to South Korea, Administration officials said today. A Commerce Department spokesman said the license for $12,000 worth of ''riot control'' equipment was issued on Wednesday.

Iran has agreed to supply natural gas to Turkey through a pipeline to be built between the neighboring countries, the Foreign Ministry said today. It said agreement on the pipeline was reached in last week's visit to Teheran by a Turkish delegation.