What was going on when I was born?

The establishment of a secure and expanding beachhead on East Falkland Island was the primary objective of Britain's amphibious operation today. The exercise may, however, be preliminary to landings elsewhere on the island, analysts said. Scorpion light tanks, Rapier surface-to-air missiles and artillery were reported to have been moved into the beachhead at Port San Carlos in preparation for an offensive. But military opinion is that the beachhead cannot be exploited to its fullest until Harrier fighter jets of the Royal Air Force are established ashore.

Secretary General Javier Perez de Cuellar said today that on the eve of the breakdown of his effort to resolve the Falkland crisis, Argentina and Britain both stiffened their positions. The final texts from the two Governments, he told the Security Council, ''did not reflect the progress which had been achieved'' inn his mediation with Argentine and British representatives. Mr. Perez de Cuellar described the major areas of agreement he thought had been reached in his 30 sessions with the two negotiators and said only four points, seemingly minor, were not settled. He did not spell out how the written texts he received from Buenos Aires and London differed from the tentative accord he thought had been reached.

The Republican-controlled Senate tonight adopted a $784 billion budget for the fiscal year 1983. It projects a $116 billion deficit, largest in the nation's history. The vote was 49 to 43. Just before passage of the document, Senate leaders led a move to reject an amendment that would have produced a balanced budget by 1985 through a sharp rise in taxes and huge cuts in military spending and benefit programs, including Social Security. ''Don't just keep saying you're for a balanced budget,'' Senator Dan Quayle, Republican of Indiana, told his colleagues. ''This is it.''

Consumer prices, checked by a steep decline in energy costs, rose only two-tenths of 1 percent in April, the Labor Department said today. The April report reflected a continuation of the sharp slowing in the rate of inflation over the past seven months. Last month's increase was accounted for by higher food and housing costs. It reversed a decline of three-tenths of 1 percent in March, which was the first drop in the Consumer Price Index in almost 17 years, but did not change the progress on inflation. For the past 12 months, the index is up 6.6 percent, the lowest 12-month increase since 1978.

President Reagan has approved a new military strategy in which United States forces need not engage those of the Soviet Union on all fronts simultaneously if a war breaks out, his national security adviser said today. Instead, the adviser, William P. Clark, speaking in broad, general terms, described a strategy that is designed to meet the Soviet military challenge by establishing priorities for United States military commitments, such as to allies in Europe, and for providing assistance to regional allies in defending themselves. The new military doctrine now endorsed by Mr. Reagan represents a significant modification of a much more embracing strategy stated by Secretary of Defense Caspar W. Weinberger. The national security adviser drew from an eight-page National Security Decision Memorandum approved this week by Mr. Reagan. He said that the ultimate objective of the Administration was to ''convince the leadership of the Soviet Union to turn their attention inward,'' suggesting that would avert Soviet threats to American interests.

British troops attacked the Falkland Islands today and established ''a firm bridgehead'' in the fighting with Argentine troops, Defense Secretary John Nott announced tonight. Mr. Nott reported that five British ships were damaged, two of them seriously, and that one Harrier jet was missing at the end of the first day of fighting. (The Defense Ministry said Saturday morning that 16 Argentine planes and four helicopters were shot down in the fighting, The Associated Press reported. The first report claimed 17 planes and two helicopters. The ministry also said British casualties were 3 dead, 2 missing and 27 wounded, the agency said, but 21 Britons were presumed dead after a helicopter crashed into the sea before the attack.)

For over five years, President Jose Lopez Portillo seemed to personify Mexico's new image of self-assurance as he presided over an unprecedented economic boom. But now, with a severe economic crisis suddenly convulsing the country, the confidence of Mexicans in the Lopez Portillo administration has been shaken and during his final months in office the President is watching his popularity tumble. The change in Mexico's mood has been dramatic. The optimism prevalent barely a year ago has been swept away by uncertainty, while rumors of the wildest nature are busily repeated by ordinary Mexicans who appear willing to believe the worst about the country.

Dominican officials fear that the new sugar import quotas imposed by President Reagan this month could wipe out any benefits the country would get from the proposed Caribbean aid plan. Sugar has long been this country's leading export, and until recently was its largest source of foreign exchange. But with the sharp decline in sugar prices, the industry has suddenly become a major financial burden. The Dominican Republic is now losing several cents on each pound of sugar it exports, even to the higher-paying United States market. By limiting that market, the United States will force the country to unload its sugar on the lower-priced world market, aggravating its losses.

The five Western nations that have been trying to mediate between South Africa and the South-West Africa People's Organization appear to be revising their tactics in an effort to revive the stalled negotiations on an independence plan. When they laid out the ground rules for their latest initiative last year, the Western nations said that the negotiations would be divided into three phases and that agreement from both sides would be needed at each stage before formal proposals were made to resolve the issues in the next one. That approach failed this month when the insurgents spurned both a proposed voting formula for the election of a constituent assembly and the phase-by-phase approach itself. Now, according to Western diplomatic sources, drafting is under way on the proposals for the next phase, which concern the machinery for enforcing a cease-fire and the role of a United Nations peacekeeping force.

A paramilitary group has threatened to kill Ambassador Edwin G. Corr of the United States if he does not leave the country within three weeks. In a statement sent to La Paz newspapers Thursday, the group, known as Sovereignty, accused the Ambassador of insulting Bolivia's armed forces.

Agriculture Secretary John R. Block said today that he would visit Canada on Tuesday and Wednesday to meet with agricultural leaders. An annoucement said, ''Among the topics tentatively set for discussion in Ottawa are the world grain situation, Canada's long-term grain agreement with third countries, grain-producer prices and the U.S. dairy situation.''

India's Marxist Communist Party and its allies headed for a landslide victory today over Prime Minister Indira Gandhi's forces in West Bengal State as ballot counting in elections to three state legislatures continued. The Communist-led front, which sought a fresh mandate after five years in office, won 110 of the 140 contests that had been decided in the 294-seat legislature. Mrs. Gandhi's Congress Party won in 30, election officials said.