What was going on when I was born?

By nightfall the town of Yamit had been ground into the desert and covered over with its sand. All but about 20 of those who had made a desperate stand against the return to Egypt of the last sector of Sinai under Israeli control were carried, shouting at soldiers, into buses that took them across what will again become an international boundary next week. The rest have promised to leave Sunday.

The decline in consumer prices, the first monthly drop since 1965 and the largest since 1953, was really a consequence of two major factors, one planned, the other unplanned and unwanted. The planned element, as the Reagan Administration rightly maintains, was its own anti-inflation policy and its persistent backing of the Federal Reserve's policy of tight money and high interest rates. The unplanned element was the recession in the United States and the world economy. That slump, probably the most severe since the 1930's, has had a powerful impact on three main sectors affecting the cost of living: - It hit energy, where the drop in domestic and world demand helped create a glut in oil supplies.

White House and Congressional budget negotiators tentatively agreed today to earmark specific taxes, such as those on tobacco and liquor, to aid the faltering Social Security System, Republican and Democratic aides familiar with the negotiations said. If the tentative agreement becomes law, it would establish an important precedent, for the first time making general tax revenues available to help finance the Social Security System. Excise taxes on liquor, beer, wine and tobacco produced $10 billion in revenues in the fiscal year 1981. It was not clear how much of this revenue or other general taxes would be applied to Social Security under the tentative agreement.

Probing a thicket of black geysers erupting from the lightless sea floor 8,600 feet beneath this ship, biologists in a three-man submarine are exploring a new world of living organisms dependent not on sunlight but on volcanic energy gushing from deep within the earth. They say this type of sulfur-based life system is far more widespread than they had previously known it to be. Dr. Robert Hessler of the Scripps Institution of Oceanography likens the findings to the experience of naturalists who accompanied Captain James Cook to Australia in 1770 and found themselves surrounded by an array of unknown plants and animals. Like organisms elsewhere on the earth, however, those forms of newly discovered life in Australia derived their energy from sunlight. They lived by basic rules that applied worldwide.

Argentine officials said tonight that two British warships violated the Argentine defense zone today by moving to within 50 miles of the sparsely inhabited Falkland Islands dependency of South Georgia. The Argentine press agency Telam quoted one Government official as saying a British attack on South Georgia, which is situated 800 miles east of the Falklands, was ''imminent.'' The officials, terming the ship's movements a violation of the Rio Treaty, said the Government had filed a protest with the Organization of American States. The treaty, known formally as the Inter-American Treaty of Reciprocal Assistance, states that an armed attack against any nation that signed the accord constitutes an attack against all.

The United States Ambassador, Deane R. Hinton, said today that the election of a right-wing coalition to lead the new Constituent Assembly would not affect the Reagan Administration's policy toward the country. Mr. Hinton said the Administration's support of the Government here ''will continue in any case.'' He said he ''would certainly hope'' that Congress would not suspend military and economic aid to El Salvador as a result of the Assembly vote. Roberto d'Aubuisson, head of the far right-wing Nationalist Republian Alliance, was named president of the Assembly Thursday night, and members of his party and two other right-wing parties were chosen for all eight other positions in the Assembly leadership. The centrist Christian Democrats received no key legislative posts.

Consumer prices declined last month for the first time in almost 17 years, falling three-tenths of 1 percent, the Bureau of Labor Statistics reported today. A sharp drop in gasoline prices, combined with declines in food and housing costs, accounted for most of the decrease in the March Consumer Price Index. For the first quarter of the year consumer prices are now up at a rate of only 1 percent annually, the slowest quarterly pace since 1965. The index rose three-tenths of 1 percent in January and twotenths of 1 percent in February. While most economists do not expect the trend to continue, the rate of inflation in the last year has declined much more quickly than forecast. The decline is being seen as an added stimulus to the hoped-for economic recovery. Many economists are now predicting that consumer prices will rise only about 6 percent this year.

The State Department appeared today to back away from a report that Secretary of State Alexander M. Haig Jr. had told a group of businessmen that Fidel Castro was ''anguishing'' over his ties with the Soviet Union because of Cuba's economic problems. A department spokesman, Alan Romberg, was asked for evidence to support Mr. Haig's statement on Wednesday that Mr. Castro was considering rejoining the West.

The Reagan Administration, which hailed the March 28 elections in El Salvador as a victory for reform over revolution, now faces a Salvadoran assembly completely controlled by rightists adamantly opposed to those reforms. The efforts that the Administration made in the last few weeks to head off such a result raise questions not only about the efficacy and the propriety of United States involvement in the Salvadoran political process, but also about whether the Administration has been acting in the best interests of the Salvadoran centrists whom it publicly supports. At stake may be the future of the Christian Democratic Party, the role of restive junior army officers and the hopes for a negotiated settlement to bring the armed leftist opposition into the Salvadoran political mainstream. U.S. Backs a Coalition The Administration, having promoted an election in which only parties to the right competed with the Christian Democrats, subsequently found itself in need of a short-term solution to make the emergent rightist leadership palatable to a questioning Congress. With that tactical goal in mind, it has supported the formation of an interim government in which the centrist Christian Democrats would coexist with the coalition of right-wing parties in control of the newly elected Constituent Assembly.

The United States is planning an early reply to Nicaragua's latest proposals for improving relations but is not yet ready to hold formal negotiations with the Sandinist Government, Administration officials said today. The officials said the United States Ambassador to Managua, Anthony C.E. Quainton, would respond to Nicaragua's call for direct negotiations early next week but would seek further clarification of the Sandinists' views. ''We want to do some more probing to make sure they're serious,'' an official said. ''We're ready to talk on any issue, but we'll have to have more exchanges at the diplomatic level before going any further.''

China has decided to restore the post of Chief of State, equivalent to the presidency, which Mao Zedong abolished as a threat to his authority during the Cultural Revolution. The decision, which had been expected by diplomats here, came to light Thursday at the opening of a new session of the standing committee of the National People's Congress, China's nominal parliament. The standing committee does all the major legislative work for the congress. At the top of its agenda is the approval of a new constitution, which will be the fourth since the Communist takeover in 1949. A constitutional revision committee announced on Wednesday that it had completed and adopted a new draft, which was originally expected last year.

A Portuguese military delegation has arrived in Mozambique for the first time since the African nation gained its independence from Lisbon in 1975. The visit, announced by the Mozambique press agency, follows the murder of two Portuguese technicians by terrorists in December and guerrilla attacks by an anti-Marxist group on the power lines of the Portuguese-built Cabora-Bassa hydroelectric dam.