What was going on when I was born?

President Reagan, saying that an agreement had been reached to end the crisis in west Beirut, ordered about 800 marines today to participate in a three-nation force to insure the safe evacuation of Palestinian and Syrian fighters from the city. In his televised statement from the White House, Mr. Reagan said the successful carrying out of the two-week phased evacuation, which is to begin Saturday, would ''set the stage'' for the rapid departure of all foreign troops -Israeli, Syrian and Palestinian - from the rest of Lebanon and for the restoration of Lebanese control over the country. He said it would also help to safeguard northern Israel from attacks from Lebanon. ''We must also move quickly in the context of Camp David,'' the President said, ''to resolve the Palestinian issue in all its aspects, as well as the other unresolved problems in the Arab-Israeli conflict. Only when all these steps are accomplished can true and lasting peace and security be achieved in the Middle East.''

The Palestine Liberation Organization returned two captured Israelis Friday, the first step in an American-negotiated plan to withdraw Palestinian guerrillas from besieged west Beirut. The Israelis, a pilot shot down on the first day of the invasion and a soldier taken from his observation post Wednesday night, were carried in a Red Cross caravan across the port of Beirut to Israeli troops in the Christian eastern section of the capital. French Foreign Legion paratroops, the first contingent of a multinational peacekeeping force that is to supervise the pullout, landed at the port at dawn today. (The French force found no sign of the Lebanese Army troops who were supposed to have taken control of the port from Israeli and Palestinian forces, according to an Associated Press report. French officers traded harsh words with their Israeli and Lebanese counterparts as the deployment got under way, with French soldiers marching to take over Israeli positions in the port area.)

A senior State Department official suggested today that the introduction of more weapons to Central America be limited and that the numbers of foreign military advisers in the region be reduced to zero. The official, Thomas O. Enders, Assistant Secretary of State for Inter-American Affairs, indicated that such steps should be part of renewed and greater efforts to achieve peaceful solutions to civil and regional conflicts in Central America. In tone and emphasis his speech to the Commonwealth Club in San Francisco seemed to be less confrontational than statements on Central American policy made soon after the Reagan Administration took office in early 1981. 'Cornerstones of Peace' Mr. Enders urged the left-wing Government of Nicaragua to discuss ways of easing tensions, saying, ''The cornerstones of peace are there.''

The stock market continued to surge yesterday, capping an exhilarating week in which both prices and trading volume reach record levels. The Dow Jones industrial average climbed a further 30.72 points, finishing the trading session at 869.26. For the week, the blue-chip average was up 81.24 points. Trading volume for the day was 95.9 million shares, bringing the week's volume on the New York Stock Exchange to 455.1 million shares.

The Soviet Union has accepted President Reagan's offer of a one-year extension of a grain sales agreement due to expire Sept. 30, Agriculture Secretary John R. Block announced today. The acceptance was delivered in writing today to the American Embassy in Moscow, Mr. Block said. He added in a statement that ''the willingness of the Soviet Union to accept this extension is proof that the Soviets believe the President's pledge that the United States will again be a reliable supplier.'' That statement was in contrast to the acrimony that has surrounded President Reagan's ban on the use of American-made or Americanlicensed equipment for the construction of a 3,700-mile pipeline to bring natural gas from Siberia to the Soviet Union.

The way in which local television stations are charged for the right to use copyrighted music has been declared illegal. Federal District Judge Lee P. Gagliardi held in a decision issued late Thursday that the payment system violated antitrust laws. His decision is intended to create competition among copyright holders to lower their fees and significantly reduce the more than $80 million that local television stations pay annually to the American Society of Composers, Authors and Publishers and to Broadcast Music Inc. At issue is the blanket licensing system under which Ascap and B.M.I. grant local stations the right to use everything from a song sung by a guest on the Joe Franklin show to the ''Mary Tyler Moore'' theme music in return for an annual fee based on a fixed percentage of the station's revenues.

The Government outlined today a multibillion-dollar package of aid to Mexico to help that country ride out its worst financial crisis in memory and make good on its huge debts to foreign banks. The package includes $1.5 billion of loans by foreign central banks, expected to become available next week, direct loans by the United States Government in the form of prepayments for Mexican crude oil and up to $1 billion of guarantees by Washington for new loans from American commercial banks. In addition, up to $4.5 billion of credits from the International Monetary Fund are expected by mid-October, according to an announcement by the Treasury Department. Efforts by Washington A news briefing by the Treasury's Deputy Secretary, R.T. McNamar, marked the first public acknowledgement by Washington of efforts under way for several weeks to help Mexico mobilize the hard currencies it will need to meet its heavy, near-term debt obligations. It is due to repay $20 billion in principal this year on foreign debt of $81 billion. An estimated $18 billion to $34 billion of that total is owed to American banks.

Around The World; Bombay Appears Calm After 2-Day Police Revolt BOMBAY, India, Aug. 20 (Reuters) - Troops and paramilitary forces appeared to have restored order to Bombay's streets today after two days of a violent police strike in which at least five people died. For the first time since the strike started on Wednesday, policemen were on the streets directing traffic and the authorities lifted a curfew in the central part of the city.

Following are excerpts from a letter from Pope John Paul II to the Roman Catholic bishops of Nicaragua. Dated June 29 and made public here Aug. 6, it was translated from Spanish by the National Catholic News Service. Since you are visible signs of unity by divine calling, I pray that you may be able to insure that the Christians of your country will not be divided because of opposed ideologies, for ''one Lord, one faith, one baptism, one God and Father'' congregated them, as they themselves are accustomed to sing, taking inspiration from the words of the Apostle Paul. And may it be that, being united by the same faith, and rejecting everything contrary to or destructive of that unity, your Christians may find themselves united in the shared Gospel ideals of justice, peace, solidarity, communion and participation, without being irremediably divided by contingent choices arising from systems, movements, parties or organizations.

A former Apollo astronaut, James Irwin, was injured today in a fall near the summit while trying to climb 16,946-foot Mount Ararat, officials said. Mr. Irwin hurt his legs and cut his forehead. He was intensive care but out of serious danger at a military hospital in Agri, 600 miles east of Ankara, a medical spokesman said.

A crowd of about 500 demonstrators surrounded a train carrying Prime Minister Pierre Elliott Trudeau of Canada and some pelted his railroad car with rocks, eggs and tomatoes when it stopped here Thursday night en route to Toronto. He stayed inside during the brief stop in Sudbury, which has 40 percent unemployment - the highest jobless rate in metropolitan Canada. The nationwide unemployment rate is 11.8 percent.

Corsican separatists set off 99 small bombs across this Mediterranean island today to dramatize their demands for independence from France. The authorities said the previous worst day of blasts was on Feb. 12, 1981, when 56 explosions were recorded. The Corsican National Liberation Front took responsibility for the explosions, which came a few hours before the newly elected Corsican Regional Assembly met and elected a moderate local leftist politician, Prosper Alfonsi, as its first chairman.