What was going on when I was born?

GENERATIONS of Americans have been brought up to believe that a good breakfast is one of life's essentials. Stoking up the body at the outset of the day, we have all been told, and told again, is as necessary as putting gasoline in the family car before starting a trip. But for many people the thought of food first thing in the morning is unappealing. So despite all the cajoling, they still skip breakfast. Between 1977 and 1983, the latest year for which figures are available, the number of people who skipped breakfast increased by 33 percent - from 8.8 million to 11.7 million - according to the Chicago-based Market Research Corporation of America. For those who feel twinges of guilt about not eating breakfast, however, there is some good news. Several studies in the last few years indicate that, for adults especially, there may be nothing wrong with skipping breakfast. ''Going without breakfast does not affect performance,'' said Arnold E. Bender, former professor of nutrition at Queen Elizabeth College in London, ''nor does giving people breakfast improve performance.''

After eight hours as Acting President last Saturday, George Bush has quickly slipped back into the relative obscurity of the Vice Presidency. Today, as President Reagan continued his recovery from cancer surgery, Mr. Bush resumed his characteristic low profile in a job that has few defined duties other than presiding over the Senate. ''Life goes on,'' the Vice President said. ''I think the news is so encouraging that's it's really going to slip back just as if the President were off on vacation somewhere.''

''At the moment, it is one of the best guarded airports in the world. That is one less place to worry about.'' -David Kyd, spokesman for the International Air Transport Association, speaking of the Athens airport.

The handling of casualties by the Air Force after the 1983 truck bombing of the Marine Corps barracks in Lebanon is described as indefensible ''medically, morally, or ethically'' in an internal memorandum prepared by an Army officer. The Air Force officer in charge of the transfer of seriously wounded marines to Europe has defended the operation. Readiness to handle such casualties in the European Command after future terrorist attacks or a larger conventional war has been sharply criticized in various internal military documents. Two memorandums written shortly after the Beirut bombing reveal a little-known story of competition between the Air Force and the Army to care for victims of the bombing who were taken to Europe, and to reap the publicity rewards from providing the care. In the course of the struggle, Air Force officers, who took charge of patient distribution, shunted wounded servicemen to an overburdened Air Force hospital while better-prepared Army hospitals were pushed into the background, according to the memorandum by the Army officer who complained of the decisions.

A plan to rehabilitate low-income housing with a $10 million bank loan has been shelved because of the Koch administration's refusal to accept a stipulation that the city stop housing families with children in a welfare hotel near Times Square. Deputy Mayor Stanley Brezenoff said yesterday that the city could not go along with the plan, first proposed late last year, because it needed whatever hotel space it could get to accommodate the growing number of homeless families. The objective of the loan was to rehabilitate 200 city-owned apartments for welfare families with children so that fewer children would have to live in the Times Square area, according to Fred Papert, the president of the 42d Street Development Corporation and the project's coordinator. Commitment From Chase The corporation is a nonprofit agency founded 10 years ago to encourage the rehabilitation of the Times Square area.

The exchange took place in a family planning workshop at the nongovernmental forum of the United Nations Decade for Women conference here. An Indian who opposes abortion told the audience that the way to control population is ''to get men to wait, to get their sexual desire under control.'' An American woman shot back, ''What if we want sex, honey?'' The incident pointed up the dichotomy between those at the conference who assert that women must control their own bodies and a small but well-organized group that calls abortion murder and any artificial method of contraception ''abortofacient'' -''abortion-making.''

Because of an editing error, an article about Pepsico Inc. in some copies of Business Day yesterday misstated the company's 1983 nonfood sales. They amounted to $996 million.

For months and years to come President Reagan's physicians will be confronting the most important uncertainty in their patient's case: Has any cancer eluded their search? Does any still lurk in the President's body, seeding new growth elsewhere? Even those closest to the case, the experts at the National Cancer Institute and the Armed Forces Institute of Pathology who are part of the team caring for Mr. Reagan at the Bethesda Naval Medical Center, said they could not tell for some time. Although Mr. Reagan's doctors spoke with guarded optimism at a news conference Monday about his chances for cure, there were clues in their words that signaled concern that the cancer might have been caught too late to prevent spread elsewhere. No Signs of Spreading ''It appears as if'' the cancer was confined to the malignant polyp within the bowel wall, Dr. Dale W. Oller, head of surgery at the Bethesda Naval Medical Center, said. Dr. Steven Rosenberg, chief of surgery at the National Cancer Institute, a member of the surgical team, said all the tests and visual inspections at surgery last Saturday showed there was ''no evidence in the President's case that the cancer has spread.''

Seven young people have been arrested and charged with conspiring to use their home computers to exchange stolen credit-card numbers and information on how to make free long-distance telephone calls, how to make explosives and how to call coded phone numbers in the Pentagon. The Middlesex County Prosecutor, Alan A. Rockoff, who announced the charges today, said the defendants also had obtained codes that would cause communications satellites to ''change position,'' possibly interrupting intercontinental communications and making legitimate phone calls impossible. Mr. Rockoff would not provide any information about the defendants, whose names were withheld because all are under 18 years old. 'Checked With Our People' Richard A. Brayall, a spokesman for the American Telephone and Telegraph Company, which owns and operates major communications satellites, said he did not think the young computer users had such information in their systems.

Can taxing the heart enhance health? ''Yes'' is the answer that continues to emerge from a growing body of research into the health effects of strenuous physical activity. Although people generally associate vigorous exercise with exhaustion and diminishing returns for their efforts, for the heart and blood vessels and for the body overall, it can mean greater resistance to fatigue and improved efficiency and stamina. The bones, joints, lungs, body weight, blood pressure, blood sugar and a person's emotional stability all stand to gain from regular exercise, as studies repeatedly demonstrate. A small but devoted group of scientists in the United States and abroad continue to do research on precisely what is happening physiologically to produce these benefits and on the types and amounts of exercise needed to achieve them. Their work shows that while physical fitness is no guarantee of cardiovascular health, it can significantly tip the balance in favor of resistance to debilitating diseases that plague the United States and other Western industrialized societies.

Reagan Administration officials said today that the Soviet Union had offered some ideas in Geneva on reducing strategic arms. But they said the concepts seemed vague and designed to perpetuate certain Soviet advantages in land-based missiles. The disclosure of the Soviet proposal came as the second round of the strategic arms talks were adjourned. A third round of the talks, which started in March, will begin Sept. 19.

The White House said today that President Reagan was ''champing at the bit'' to return to work despite the disclosure Monday that a tumor removed from his abdomen was cancerous. Mr. Reagan conferred with Donald T. Regan, his chief of staff, for 25 minutes today and spent most of the afternoon with his wife, Nancy, in a suite at Bethesda Naval Medical Center in Maryland. At one point, Mrs. Reagan accompanied the President for a walk up and down the hall, according to her spokesman, Jennefer Hirshberg. The White House spokesman, Larry Speakes, said that despite ''a little discomfort,'' as a result of the surgery Mr. Reagan underwent Saturday, the President ''continues to recover very well.'' The discomfort occurs when Mr. Reagan ''gets up in bed or rises to get in a chair,'' he said.