What was going on when I was born?

The end of the 15-month curb on grain exports to the Soviet Union was probably President Reagan's most important single foreign policy decision so far, but there was no indication today from people in the Administration that it would do anything but undercut Washington's proclaimed policy of toughness toward Moscow. Hours after the decision was disclosed, Secretary of State Alexander M. Haig Jr. inveighed, as he has done repeatedly since taking office, about the Soviet Union's posing ''the greatest danger'' to the world. He promised that the United States would never accept Soviet intervention in countries such as Afghanistan. But his aides acknowledged that Mr. Haig's speech seemed to have a hollow ring because of the decision to end the grain curbs, which were imposed by the Carter Administration in retaliation for the Soviet move into Afghanistan in December 1979.

For nearly two years, two tribes, one established and one new to this fishing village on the grayish, sunflecked waters of Galveston Bay, have been locked in a kind of territorial struggle as old as the species. Now the struggle is approaching a critical point. One tribe is made up of American shrimp fishermen. The other consists of Vietnamese refugees who, having fled their country after the fall of Saigon in 1975, flocked to the Gulf Coast to make their living as shrimpers, too. Operating from a stretch of docks that has been dubbed ''Saigon Harbor,'' they now outnumber the Americans. The problem, according to the white shrimpers, is that their livelihood is jeopardized because the shrimp fishing hereabouts will simply not support everybody. In the resulting dispute, two Vietnamese shrimp boats have been burned, and hostility and suspicion are rife in the twin fishing towns of Seabrook and Kemah.

Under a barrage of hostile questions from the prosecutor, Senator Harrison A. Williams Jr. maintained yesterday that he had neither said nor implied to undercover agents that he would arrange to get Government contracts for a titanium mine in which he had accepted stock. He continued to insist this was so even after the prosecutor, Thomas P. Puccio, played a portion of a 1979 videotape in which the New Jersey Democrat told the agents there would be ''no problem'' in using his relationships with top Government officials in trying to get the contracts. The tape was made secretly as the Senator was meeting in a Virginia motel with the agents, one of whom posed as an Arab sheik. It is a key piece of prosecution evidence in the 61-year-old Senator's Abscam bribery trial, which ended its fourth week yesterday in Federal District Court in Brooklyn. The cross-examination began in late afternoon.

A Federal judge ruled yesterday that a New York City pension system, which assumes that women live three years longer than men, illegally discriminates against women employees by requiring them to make higher contributions even though they receive lower monthly benefits when they retire. The judge, Mary Johnson Lowe of District Court in Manhattan, ruled in a 31-page opinion that the higher contributions and lower benefits violated the Civil Rights Act of of 1964. Judge Lowe said she would not decide what damages should be awarded before further hearings or a full trial. Her decision yesterday was based on legal motions only.

The number of measles cases reported in the United States so far this year is 80 percent below the comparable period last year, a drop so dramatic that the Federal Centers for Disease Control predicts that, except for imported cases, the disease will be eliminated by the end of 1982. The Atlanta-based agency said yesterday that even though the measles season was well under way, there had been only 778 known cases in the first 14 weeks of this year, as against 3,897 cases in the comparable period of 1980. The season ordinarily peaks in April. Dr. Alan Bloch, a medical epidemiologist for the disease control agency, said the precipitous drop was an indication of the success of nationwide vaccinations under the Measles Elimination Program. The program, using a vaccine first licensed in this country in 1963, was initiated two and a half years ago by the Department of Health, Education and Welfare, now the Department of Health and Human Services.

Three nights of freezing temperatures in the last two weeks have severely damaged the apple crop in New York State, the second largest producer of apples in the United States and a major supplier of apples for export. Reports from fruit growers and experts in the state's three major apple-producing areas - the Hudson Valley, the Champlain Valley and the lee of Lake Ontario south of Rochester - all indicated that the crop this fall would be down substantially and that the price to consumers would rise accordingly. The freeze affects all the varieties of apples in the state, where the McIntosh is the major one produced. ''It's the worst freeze in the Hudson Valley since 1945,'' said Benjamin Bartolotta, who has 800 acres devoted to apples and other fruit in his orchards in Livingston, in southern Columbia County.

Secretary of State Alexander M. Haig Jr. today called the Soviet Union ''the greatest source of international insecurity.'' In his first public speech since taking office, Mr. Haig outlined what he said was the philosophy behind the Reagan Administration's ''new direction'' in foreign policy. There were no new developments or approaches in the speech, however, which dwelt heavily on criticism of the Soviet Union.

President Reagan today lifted the 15-month curb on United States grain exports to the Soviet Union, fulfilling a campaign pledge but warning that his Administration was not reducing its determination to stop Soviet ''acts of aggression wherever they take place.'' Mr. Reagan announced his decision to the Cabinet in a closed session this morning that marked his first appearance in the West Wing of the White House since the attempt on his life March 30. After signing the documents, he returned to the family quarters and the decision was made public by the deputy press secretary, Larry Speakes. The limitation on grain sales was imposed by President Carter on Jan. 4, 1980, as punishment for the Russian intervention in Afghanistan. Under the ban, the Russians have received only 8 million of the 25 million metric tons of grain they were promised in each of the last two years.

Secretary General Kurt Waldheim has privately promised Southeast Asian nations that he will call a longdelayed conference aimed at bringing peace to Cambodia, officials disclosed here today. But Mr. Waldheim has reportedly warned that the conference will probably fail because the Soviet Union and its allies, Vietnam and Laos, have said they will not attend. It is now up to the members of the Association of Southeast Asian Nations -Thailand, Singapore, Indonesia, Malaysia and the Philippines - to decide whether they want Mr. Waldheim to go ahead. Diplomats from the five nations have indicated that they do.

A senior West German politician who visited Latin America this month says that he was told by Fidel Castro that Cuba had shipped arms to insurgents in El Salvador but that the shipments had ended. The official, Hans-Jurgen Wischnewski, deputy chairman of the Social Democratic Party, was quoted by a party spokesman as saying that Mr. Castro had told him that the Soviet Union had not been involved in sending arms to the guerrillas.

A new trial has been ordered for two Cubans charged with the murder here of Orlando Letelier, a Chilean exile leader. Last September, a United States Court of Appeals overturned the conviction of the two Cubans, Guillermo Novo Sampol and Alvin Ross Diaz, on the ground that United States District Judge Barrington D. Parker, who sentenced the two to life imprisonment in 1979, erred in admitting testimony from ''Government informants'' who were prisoners in the same jail as the two Cubans. Judge Parker will preside at the second trial.

President Jose Napoleon Duarte said today that he was willing to hold talks with guerrilla leaders provided there were no preconditions. However, he said that an offer by the Farabundo Marti National Liberation Front to hold talks if certain conditions were met was a political maneuver.