What was going on when I was born?

An agreement has been reached to limit the outside income of physicians and dentists on the faculties of medical and dental schools run by New York State, officials said yesterday. The agreement, between the state and the union representing faculty members, is similar to ones in most other states and at many of New York's private medical schools. It is primarily aimed at physicians, state officials said, and stipulates that in most cases they can earn no more than 150 percent of their base faculty salaries in outside income. The accord also requires that the faculty members must pay the cost of nurses, equipment and administrative upkeep if they operate a private practice in a state facility.

New York City's Department of Investigation has begun a review, described as routine, of the background of the Commissioner of Ports and Terminals, including her role with a family- owned marine company that has a record of disputes with environmental agencies. The company, which cleans ships of oil and chemical wastes, is currently under a New Jersey ''notice of prosecution'' charging it with refusal to furnish records upon request and to allow authorities to take test samples, among other violations. It has also been accused of improperly discharging wastes into New York Harbor. The company is challenging the state's right to the information it seeks and says it is seeking to comply with environmental regulations. A spokesman for Mayor Koch said that the Mayor had not been aware of any regulatory actions involving the former company of the Commissioner, Susan Frank, but that ''it will be checked thoroughly by the Department of Investigation.''

With the proposed merger of Republic Steel and the LTV Corporation, heavy layoffs at United States Steel and third-quarter losses predicted for nearly all the major producers, the industry has been even more turbulent than usual in the last few weeks. But there is apparently some good news around the corner. Analysts predict that the industry's limping sectors - structural elements and steel plate - will improve early next year as the anticipated upswing in capital spending materializes. They say this should help revive U.S. Steel and the Bethlehem Steel Corporation, now the industry leaders, and should improve the prospects of LTV Steel, as the merged company will be called if shareholders and the Federal Government approve the agreement.

''This is the first time in the history of the Congress and the executive branch that we have worked out jointly an arms control proposal in which we are truly united.'' - Senator Charles H. Percy, Republican of Illinois. (A1:3.)

A gold trading company, whose chairman killed himself the day before he was scheduled to deliver financial records to investigators, filed for bankruptcy yesterday, reporting that between $55 million and $60 million in precious metals was missing from its vaults. Lawyers for the company, Bullion Reserve of North America, told investigators for the State Attorney General, Robert Abrams, that a fortified repository in Utah that should have contained about $60 million only held $900,000, a spokesman for Mr. Abrams said. The spokesman, David Fishlow, said that counsel for the precious metals company reported that the concern had lent its chairman, members of his family and a number of subsidiaries about $40 million in the last year.

The Soviet Union published a point- by-point dismissal of the latest U.S. proposals on limiting medium-range nuclear weapons in Europe. Page A5. WASHINGTON, Oct. 3 - President Reagan told key members of Congress today that he would propose a new concept at the next round of strategic arms negotiations with the Soviet Union. Under the plan the deployment of new warheads would have to be accompanied by the destruction of older ones.

BERKELEY, Calif. THE first microscope able to take directly interpretable pictures of atoms within solids has begun operating here, providing scientists with an extraordinary new window on the internal structure of matter. The instrument, an atomic resolution microscope, is being used by materials experts to improve basic understanding of why solids behave as insulators, semiconductors and metals. And it promises to show, in greater detail than ever before, ways in which materials fail and, by extension, ways to design better computers, catalysts and ceramics, to name but a few applications. The ARM, as it is called, is one of two advanced high voltage electron microscopes at the newly completed $7.5- million National Microscopy Center at the Lawrence Berkeley Laboratories. The federally financed facility, which was dedicated Friday, is expected to give American researchers a leg up in the competition of developing new technologies based on experimental materials.

Chad, struggling at home with a civil war and a drought, is having a hard time keeping its United Nations mission open and its diplomats fed. The situation has improved somewhat since the summer, when the diplomats' telephones were cut off and private charities gave them groceries, but the future of the mission is uncertain. Rent remains upaid at the mission office and at the residences of several of the delegates. Eviction procedures on apartments in Corona, Queens, were initiated but were halted because members of the delegation have diplomatic immunity.

AMARKED decrease in casual or promiscuous sex has been occurring in the United States in the last several years, many experts believe. Psychiatrists, public health workers and law-enforcement officials say their suspicions are being confirmed that such a decrease has been taking place. The reasons, they say, go well beyond the relatively new fear of such diseases as acquired immune deficiency syndrome (AIDS) or herpes and include a broader kind of retrenchment from the sexual revolution of the 1960's and 70's, according to the experts. These students of contemporary social behavior say the shift away from the kind of indiscriminate sexual behavior that often involves people who do not know each other well or are not engaged in an otherwise close or intimate relationship, is occurring both among heterosexuals and homosexuals. However, the change is particularly discernible among homosexuals who have adopted a much more conservative sex life in response to anxiety and outright fears about contracting AIDS, which has struck more than 2,250 people in the United States and Puerto Rico, three-quarters of them homosexuals. More than 900 of them have died as a result of the disease.

The White House today announced the indefinite postponement of President Reagan's planned visits next month to the Philippines, Indonesia and Thailand, citing the need for Mr. Reagan to be in Washington to deal with Congress on the budget and other issues. Mr. Reagan still plans to visit Japan and South Korea around mid-November, Larry Speakes, the White House spokesman, said. Mr. Speakes said the President's decision ''does not alter in any way the fundamental positive relationship'' between the United States and the three countries dropped from the President's itinerary. Concern Over Philippines The President decided to defer his trip last Thursday evening, White House officials reported, amid rising concern among several advisers about turbulence in the Philippines, where anti-Government demonstrators have clashed with Government forces. Nancy Reagan, the First Lady, was also understood to be fearful of the conditions in the Philippines, particularly after the assassination of former Senator Benigno S. Aquino Jr.

TODAY, as in all past autumns, millions upon millions of leaves are being transformed from green to a multitude of brilliant yellows, scarlets and russets. But a new interest has been awakened in the process; some researchers now see in it possible clues to aging, not only in plants but in animals - including man. While some of the most basic steps in the changing of leaf color are not yet understood, recent research has uncovered tantalizing details. It has long been known that autumnal color changes result from a breakdown of chlorophyll, the green substance in leaves. It now appears that this occurs when proteins to which the chlorophyll molecules are bound break up into the amino acids of which they are formed. When the chlorophyll is no longer bound to a protein, it disintegrates, losing its green color.

Orders to factories during August rose 1.1 percent, an improvement after the previous month's decline but the smallest gain since the economic recovery began, the Commerce Department reported today. Economists said the smaller gain in orders was consistent with other reports suggesting that the economy has slowed to a more moderate growth rate in the third quarter after the vigorous pace of activity in the second quarter as the recovery was taking hold. ''The downswing that was occurring in the summer months is evidenced by the slower advance of orders,'' said Tom Robinson of Merrill Lynch, Pierce, Fenner & Smith Inc.