What was going on when I was born?

Israel's Cabinet voted unanimously today to withdraw from Sinai on Sunday, as required by the peace treaty with Egypt. Hours after the decision, the army moved against militant Jewish protesters in the northern Sinai town of Yamit, evicting them by force. In Cairo, the Egyptian Cabinet hailed the decision as an important step that alleviated concern in recent days about a possible hitch in the last phase of the Sinai withdrawal. (Page A14.)

The nine-month-old cease-fire between Israel and the Palestine Liberation Organization was shattered today as waves of Israeli planes attacked guerrilla positions south of Beirut hours after an Israeli soldier had been killed by a land mine in southern Lebanon. The jets pounded Palestinian-controlled villages south of Beirut. Lebanese Government sources said at least 23 people had been killed and an unspecified number wounded. There was no indication how many of the casualties were guerrillas and how many civilians.

The gross national product, the country's broadest measure of economic activity, fell at a 3.9 percent annual rate in the first quarter, confirming that the recession continued through March, the Commerce Department reported today. But the economic downturn, which started last July and has pushed unemployment to 9 percent, continued to slow the rate of inflation. A G.N.P. price index rose only 5.6 percent in the first quarter, the smallest increase in four years, following an 8.6 percent advance in the fourth quarter of 1981. Similarly the better-known Consumer Price Index rose at an annual rate of 3 percent in February, also much less than in recent months. The index for March will be announced Friday.

New factory orders for durable goods rose 1.9 percent in March, making it the first time since last summer that such orders have risen for two consecutive months, the Commerce Department reported today. As a leading economic indicator, the rise in durable goods orders for March was viewed by some economists as a hopeful sign that the economy might begin its recovery from the current recession in the next few months. Robert Ortner, the Commerce Department's chief economist, called the durable goods figures ''one of the more important indicators we have'' and said that he was encouraged by the March results.

A preliminary examination indicates that a .22-caliber shell casing found in the van of a New Jersey man was fired from the same gun that killed a Federal witness and three CBS employees, Police Commissioner Robert J. McGuire disclosed last night. The Commissioner said the casing also matched a spent shell that had been recovered in the car of a friend and former co-worker of the Federal witness. Police officials have said they believe that the friend, who disappeared in January, has been slain. Mr. McGuire said blood stains and other forensic evidence had been found in the van driven by Donald J. Bowers of Keansburg, who was arrested Monday in Kentucky. Mr. Bowers, 46 years old, has become the central figure in the investigation of the four slayings and the disappearance of the witness's friend. The New Jersey man, who is also wanted as a fugitive in another case, was returned to New York last night after waiving extradition. Escorted by two New York City detectives, he got off a Piedmont Airlines plane at Newark International Airport at 9:31 P.M.

International The truce in Lebanon was shattered as Israeli jets bombed Palestinian guerrilla positions south of Beirut hours after an Israeli soldier was killed by a land mine in southern Lebanon. Lebanese Government sources said at least 23 people had been killed in the raid. Two Syrian MIG-23's were shot down by Israeli planes. (Page A1, Col. 6.) Washington urged the P.L.O. not to retaliate against Israel for the bombing raids in Lebanon in an effort to avert a breakdown in the nine-month-old cease-fire negotiated by the United States. Officials confirmed that President Reagan had reassured Israel that, in return for its withdrawal from Sinai Sunday, Washington would maintain Israel's military superiority over the Arabs. (A15:1.)

Charles L. Brown, chairman of the American Telephone and Telegraph Company, urged more than 5,000 shareholders attending the company's annual meeting here today to continue lobbying against a proposed House bill that A.T.& T. has said would place undesirable restrictions on it after divestiture of its local operating companies. Speaking directly to shareholders for the first time since the announcement of a proposed settlement of the Justice Department antitrust suit against A.T.& T., Mr. Brown sought to reassure a puzzled but generally supportive crowd, many of whom wore buttons provided by A.T.& T. reading ''H.R. 5158 Is A Wrong Number.'' Swelled by interest in the settlement and the East Coast location of the meeting, this year's attendance of 5,112 persons was almost four times higher than the 1,400 shareholders at last year's meeting in Houston, and the crowd overflowed the main auditorium of the convention center here.

A news item in Notes on People yesterday about the composer Arthur Schwartz omitted the name of the lyricist for the songs ''Dancing in the Dark,'' ''That's Entertainment,'' and ''You and the Night and the Music.'' He is Howard Dietz.

Atop Galena Summit, 26 miles north of here, the county snowblowers are still working Highway 75, cutting back the sheer 15-foot cliffs of snow that line the approach to the pass like the walls of a tunnel. ''Considering it's past the middle of April already, this spring is going to be a real humdinger,'' said Jerry Seiffert, the Mayor of Ketchum, the central Idaho town that adjoins the Sun Valley ski resort. ''No matter how you cut it,'' he added, ''when all this stuff melts, someone is going to get wet, very wet.'' All across the Western mountains, from the rugged Northern Rockies to California's Sierra Madre, snow levels in the high country this April are at near-record or record levels. Ski resorts are extending their season far into spring, and for Western farmers, fishermen, and river rafters, the thick mountain snow pack assures what the United States Agriculture Department's Soil Conservation Service calls ''good to excellent water supplies'' over the dry summer months. That means the spring runoff will help top off reservoirs and water storage facilities throughout the region.

The Organization of Petroleum Exporting Countries is producing only 15.85 million barrels of oil a day, more than a million barrels below the group's official ceiling, its president said yesterday. The announcement suggested that OPEC might be succeeding in its campaign to curb output substantially, exerting upward pressure on prices. Evidence that prices are, indeed, firming includes a rise in the price of crude oil on the spot, or noncontract, market, of about $2 a barrel in the last month, to approximately $31. In the last week, heating oil futures have also risen, by more than a cent a gallon, after months of almost steady decline. At the same time, a number of independent refiners have raised gasoline prices, by a quarter of a cent to 4 cents a gallon.

The continuing recession caused a 3.9 percent drop in the G.N.P. in the first quarter, after a 4.5 percent drop the quarter before. The stagnation was attributed to inventory reduction. (Page A1.) Durable goods orders rose 1.9 percent in March after a 3.5 percent gain in February, the first two-month rise since July. (D1.)

The big push that could determine its survival has begun at Pan American World Airways. A major ad campaign to lure people to its international destinations is now in place as are many union concessions that should enable the carrier to increase its operations by 12 to 15 percent without raising costs. In addition, a few encouraging trends, such as lower fuel prices and an upturn in travel, have developed since C. Edward Acker, the carrier's chairman and chief executive officer, adopted the bold strategy last fall of trying to fly the airline out of its huge operating losses, which totaled $364 million for the company last year. ''In terms of fuel we're looking a lot better,'' said Mr. Acker, who came to Pan Am last September from Air Florida. Since Pan Am has one of the oldest fleets in the industry and has not ordered any of the new, more efficient planes, a continuing drop in fuel prices is important to its long-term health.