What was going on when I was born?

Lillian Carter, the 85-year-old mother of former President Jimmy Carter, died of cancer yesterday in Americus- Sumter County Hospital in Americus, Ga., where she had been hospitalized since Tuesday. The 39th President was at his mother's side when she died shortly after 5 P.M., as were Mrs. Carter's two other living children, Billy Carter and Gloria Spann, and Jimmy Carter's wife, Rosalynn. Mrs. Carter's other daughter, Ruth Carter Stapleton, died of cancer Sept. 26. Her physician, Dr. Paul Broun, said Mrs. Carter died of cancer that had spread to the bone. On June 29, 1981, Mrs. Carter underwent a modified radical mastectomy after a malignant tumor was discovered in her left breast. Mrs. Carter, known to her neighbors as Miss Lillian, was a nurse, a Peace Corps volunteer, an unofficial ambassador and a supporter of civil rights and women's causes. She also said what was on her mind.

''I hope we will succeed in saving our country, which we have always compared to Switzerland and always called the Switzerland of the Orient.'' - Pierre Gemayel, founder of Lebanon's Christian Phalangist Party and militia. (A1:4.)

The leaders of Lebanon's main religious and political factions gathered here today in preparation for their long-awaited peace talks. If the meeting, known as the national reconciliation dialogue, begins Monday as scheduled, it will be the first time that all of Lebanon's factional leaders have come together around a single negotiating table since the country's civil war broke out in April 1975. ''I hope we will succeed in saving our country, which we have always compared to Switzerland and always called the Switzerland of the Orient,'' said Pierre Gemayel, the 78-year-old founder of the Christian Phalangist Party and militia, as he arrived here. ''We live in hope. We have been hoping for 10 years.''

THE National Horse Show at Madison Square Garden may have a certain mystique, but it is a mystique of high society, not of athletes and horses. The image regularly associated with the annual show is of silver-haired, hawk-nosed gentlemen in tuxedos and elegant, diamond-decorated women in expensive furs, offering polite applause from ringside boxes as the polished horseflesh parades before them. The image could just as easily be of sweat and straining muscles and dirt under the fingernails. It could feature intense-looking riders making split-second judgments in the face of obstacles 6 and 7 feet tall, and the powerful, 1,400-pound horses who react to those judgments boldly. The image could be of Leslie Burr, who broke her collarbone in a fall from her horse two weeks ago but is so determined to win the rider- of-the-year ranking that she will compete over the National's daunting jumps this week with her shoulder taped.

The American force on Grenada has been reduced from 6,000 to about 5,300, a Defense Department spokesman said today. The spokesman said 700 Army Rangers had been withdrawn from the Caribbean island and were returning to bases in the United States. In another development, a senior State Department official said the United States did not dispute Cuba's statement that there were only 784 Cubans on Grenada when American forces invaded the island on Tuesday. The Reagan Administration said Friday that it believed 1,100 Cubans were there.

The Rev. Jesse Jackson said yesterday that he would formally announce his candidacy for the Democratic Presidential nomination Thursday at a news conference in Washington. ''Our position has been that we have been an unofficial candidate in the Democratic primaries,'' Mr. Jackson said in Atlanta. ''I expect to become an official candidate.'' In a speech at Morehouse College, the civil rights leader repeatedly cited a need for new leadership and a new coalition within the Democratic Party. He pledged to work for parity for ''blacks in a white society'' and the defeat of President Reagan.

The United States has agreed in principle to compensate Common Market countries for injuries caused by Washington's restrictions on specialty steel imports. As a result, American and European trade officials say, the once testy compensation negotiations are going much better and may be settled by Nov. 30. Last July, President Reagan announced four years of tariffs and quotas on specialty steel. Officials from the European Economic Community then asked for compensation for injuries they said would result. They threatened to raise tariffs on American goods if there was no agreement by the end of November.

Economic Analysis The emerging foreign debt problem of the Philippines does not warrant the concern that other Asian nations may not be able to service their debts, according to bankers and international economists. Such concern may be understandable, these experts concede, in view of the regional dimensions of the debt crisis in Latin America. But they point out that Asia's approach to development over the past decade has been fundamentally different from that in Latin America. ''As a group, the Asian countries are much more export-oriented, have remained much more competitive and have stronger governments than the Latin American nations,'' said Rimmer de Vries, a senior vice president at the Morgan Guaranty Trust Company.

United States forces patrolled here today amid signs that this Caribbean island capital was approaching near normal life. Sniping continued from the hills around the city. But less than a week after United States and Caribbean forces invaded, electricity has been fully restored and with it an adequate water supply. Food was available although some stores have been looted and supplies remained a problem. Local telephone service was restored although international service was still out.

A Reuters dispatch in the Company News column in Business Day last Wednesday incorrectly reported Mattel Inc.'s financial results for the six months ended July 31, 1982. The company earned $31.2 million.

The Jets showed today why they are one of the National Football League's most enigmatic teams. After losses in three previous games, they defeated one of the best teams in the league, the San Francisco 49ers, 27-13. And they did it with a style and fortitude that was missing in their last and most embarrassing loss, when they led Atlanta, 21-0 through three quarters, only to fall, 27-21. This time, on the soggy field in Candlestick Park, the Jets took over the lead in the second quarter and kept it, playing one of their best defensive games of the season in the process. The 49ers were held to 312 yards offense, their lowest total of the season, and did not score in the first and fourth quarters, the periods in which the Jets had given up the most points through their first eight games. It was also the first game in six weeks in which the Jets were not intercepted.

Texas Instruments' move out of the home computer business may be of little help to its competitors, except for I.B.M. Page D4. The losing battle of Texas Instruments Inc. in the home computer market has taken a severe toll on the company's finances, its reputation and its employees. Yet more than one million other people - the owners of the Texas Instruments 99/4A home computers - will suffer as well. They are likely to find it much more difficult to get their machines repaired and to find new programs and peripheral equipment, such as data storage devices and printers, to use with the machines. Their situation, will be somewhat akin, but perhaps more severe, to the situation confronting those who own eight-track tape players and find that many of the latest recordings are no longer available in that format, analysts say.