What was going on when I was born?

The American Home Products Corporation, the maker of Anacin and several other well-known consumer products, has agreed to purchase $250 million worth of advertising air time from NBC-TV over the next three years, the companies announced yesterday. The agreement, believed to be the largest forward commitment made by an American advertiser for television time, is apparently intended to shield American Home, the fourth-largest corporate spender on advertising, from rate increases over the next three years. The three major television networks are believed to be considering a 15 percent increase in advertising rates for the new season. The agreement, which would cover time in all parts of the broadcast day, is scheduled to begin this fall when the second of two contracts for two years between NBC and American Home expires.

A New York State appellate court yesterday voided the guilty plea of a Brooklyn dentist who admitted to sexually abusing an investigator posing as a patient. The court held that a videotape camera surreptiously installed in the ceiling of the dentist's office - and that had recorded the sexual abuse of the woman - had been put into place too long after the issuance of a warrant authorizing it. According to the appellate court, state law requires the installation within 10 days of the issuance of the warrant, whereas the camera in this case was installed 17 days after the warrant was issued.

The United States Government has begun a formal investigation into possible price fixing by six Japanese companies selling sophisticated semiconductor computer chips in the American market, Japanese and American Government officials said here today. The investigation by the Justice Department is focused on the practices of the companies in marketing 64K random access memory chips - the most advanced of the computer memory devices now available. John P. Stirn, a spokesman for the United States Embassy, said the embassy had notified Japan's Foreign Ministry of the investigation last Thursday. The six Japanese companies under investigation are: Hitachi, Nippon Electric, Toshiba, Fujitsu, Mitsubishi Electric and Oki Electric. They are Japan's largest makers of semiconductors, which are gridlike circuits etched on tiny chips of silicon. They are used for calculation and information storage, the basic functions of computers.

Two-thirds of New York City's poor people do not have home telephones, in part because of rising costs, State Attorney General Robert Abrams said yesterday. He added that 25 percent of all homes in the Bronx and 41 percent in Brooklyn's Williamsburg section did not have telephones. As a result, Mr. Abrams told a state Public Service Commission hearing, ''hundreds of thousands of New Yorkers must depend on neighborhood pay phones.''

IN another era, when society was firm in its view that automobile mechanics and plumbing were jobs for men and cosmetology and secretarial work were jobs for women, the public schools set up systems of vocational education reflecting these divisions. Now, however, as the presumption of segregating careers by sex has lost favor, the schools are under pressure to change those systems. The impetus is not only the demand for equal treatment, but also the fact that traditionally male fields usually pay much higher salaries. The issue is perhaps most sharply focused in New York City, where the school system, with almost one million pupils, is so large that entire high schools were created to teach a single trade.

Evans as the group moved single file along a narrow path in the woods behind the Manomet Bird Observatory here. Strung vertically along the side of the path was a shoulder-high black nylon net and trapped in its fine, almost invisible webbing were six robins struggling vainly to free themselves. Moving swiftly and surely, Mr. Lloyd-Evans, the observatory's senior staff biologist, and two assistants began methodically and as delicately as possible to extricate the birds from the webbing. The birds, though complaining vocally, seemed unharmed. When all the robins had been freed and carefully placed in bags, they were taken to the observatory's laboratory, where a record was made of each bird's species, sex, weight, size, approximate age, fattiness and other characteristics. A thin, numbered aluminum band was then placed on each bird's leg and the bird was released.

President Reagan is expected to resolve a protracted and heated Administration debate later this week by authorizing a one-year renewal of the grain trade agreement with the Soviet Union, several Administration aides said today. Under the President's announcement, the Soviet Union would continue to be obligated to buy a fixed amount of grain for the year beginning Oct. 1. But the Administration aides, who declined to be identified, said Mr. Reagan was undecided whether to raise the obligated amount from the current level of 6 million metric tons a year. An increase has been sought by Agriculture Secretary John R. Block.

President Reagan is expected to authorize a one-year renewal of the grain trade accord with Moscow later this week, Administration officials said. They said Mr. Reagan would continue Moscow's obligation to buy a fixed amount of grain for the year starting Oct. 1 but is undecided as to whether to increase that amount. (Page A1.) Washington is looking into the pricing practices of six Japanese companies selling sophisticated semiconductor chips on the American market. Officials said the companies are suspected of having acted collectively to fix prices and restrict chips in violation of American antitrust law. (A1.)

International The U.S.-Soviet grain accord would be renewed for one year under an authorization that Administration aides expect President Reagan to announce this week. Under the expected announcement, Moscow would continue to be obligated to buy a fixed amount of American grain for the year beginning Oct. 1. (Page A1, Column 6.) The first domestic hijacking in China was officially acknowledged by the Peking authorities. The Chinese passengers and crew members fought a desperate midair battle with the five hijackers, who reportedly blew a hole in the side of the plunging airliner before being subdued. (A1:2-3.)

educated city boy from White Plains, Joel Silverstein, M.D., might seem slightly out of place in this village of 2,076 people. But here he is, a 37-year-old specialist in internal medicine, building his practice among the farmers and townsfolk of this northern Vermont area, hauling and splitting wood and raising a family and golden retrievers on a 100-acre farm just outside of town. He says he loves it, even if his wife, Vicki, complains about the dearth of Chinese restaurants. Dr. Silverstein is a sophisticated new version of the old country doctors who once ministered to the medical needs of these remote reaches. As such, he typifies a growing breed of highly trained young doctors, many of them specialists who, for the first time in American medical history, are dispersing themselves in large numbers into smaller towns and cities and rural areas. Such towns have long been medically underserved because doctors had preferred urban life. Just a decade ago, Morrisville, where about 22,000 people in a large surrounding area go for medical care, had only a half dozen full-time physicians, all general practitioners except for one general surgeon. Today, even though the population has grown only slightly, there are more than two dozen doctors in the area, including a pediatrician, three surgeons, three internists, two radiologists, four emergency room specialists, a pathologist, an anesthesiologist, four family practice specialists and a psychiatrist.

Thanks to the discipline imposed by martial law, Poland's coal production is booming again. But whether the country can soon regain its position as a leading coal exporter, considered vital for the improvement of its sagging economy, seems highly doubtful. To their immense frustration, Poland's military authorities are finding it hard to sell their coal in a world glutted with energy, especially since the United States, along with Australia and South Africa, has taken many of Poland's traditional markets. ''Re-entry into the Western market is difficult,'' said Stanislaw Zajac, director of economics at Weglokoks, the state coal export company with headquarters in this southern Polish mining town. ''Our customers promise to go back to Polish coal, but not for a while. They don't need it so much.''

Americans spent $287 billion for health care last year, representing a record 9.8 percent of the gross national product, the Department of Health and Human Services reported today. Health spending from all sources, including Government agencies and private insurance companies, averaged $1,225 a person, the department said in its annual survey of health expenditures. Of that amount, $524, or 42.8 percent, was spent by Federal, state and local governments. Total health expenditures, public and private, increased 15.1 percent from 1980 to 1981, the department reported, noting that the G.N.P. increased by only 11.4 percent in the same period.