What was going on when I was born?

BUYERS looking for a creative way to buy themselves shelter in New York City often consider purchasing a small rental building. The object is to obtain an apartment or two for oneself while counting on the rent from other apartments to cover all or most of the building's costs. The depreciation allowance permitted on the rental portion of the building acts as a tax shelter. Owner-occupied buildings with 6 to 10 units are being sold for less than $200,000 in the Bay Ridge section of Brooklyn and in Jackson Heights and Corona, Queens, brokers report. Prices vary depending on condition, cash flow and location.

Early in September the ''gift box'' that has hidden Bergdorf Goodman's Fifth Avenue entrance since March is due to come off, revealing the results of a six-month facelift.

THE QUALITY OF MERCY Cambodia, Holocaust and Modern Conscience. By William Shawcross. 464 pp. New York: Simon & Schuster. $19.95. FROM late 1978 through 1980, Cambodia held center stage among the world's disaster areas. United States involvement from 1970 to 1975 in its civil war had been only a ''sideshow''; Khmer Rouge terror from 1975 to 1978 had not been ignored, but while it was at its height, it did not register significantly on the world's consciousness. What propelled Cambodia into the limelight was the outbreak of war between the Khmer Rouge (the name by which Cambodia's Communist revolutionaries were known) and their former allies, the Vietnamese Communists. As William Shawcross, the author of ''Sideshow: Kissinger, Nixon and the Destruction of Cambodia,'' writes in ''The Quality of Mercy,'' ''Massive abuse of human rights alone had failed to win worldwide attention in the way that open schism and warfare within the Communist bloc did.'' As a way of legitimizing its conquest of Cambodia, Vietnam and its Soviet bloc allies helped bring the world's attention to the atrocities committed by

NEW HAVEN BACK in the 1700's New Haven's harbor bustled with activity. Shops lined the waterfront, which ran right into the downtown area. People regularly worked there, shopped there, or just strolled past. Today the harbor no longer bustles. Instead, people often remark, it smells. Like the harbors of many other American cities, it has grown isolated from the center of town and the center of activity.

At this moment, the Goodman Theater of Chicago may be the most exciting theater in America. In the last six months, it has spawned and sent to New York both ''Glengarry Glen Ross,'' for which David Mamet won the Pulitzer Prize, and ''Hurlyburly,'' the David Rabe drama that must be considered a strong contender for the prize next year and meanwhile is one of the choicest tickets in Manhattan. Then there are the less tangible, more private measures of success. French television wants to interview Gregory Mosher, the Goodman's artistic director. Mark Medoff, the author of ''Children of a Lesser God,'' sends his new play to the Goodman, unsolicited. Marvin Hamlisch calls to see if the theater wants to stage his musical ''Jean Seberg.'' To invert the adage, everybody knows you when you're up and in.

''God is great,'' the villagers in Borj Rahal cried as they carried the body of Hassan Sahli out of the mosque and down the dusty hillside to his grave. ''Israel is the agent of Satan.'' The death of Mr. Sahli last month - villagers say he was shot to death by Israeli soldiers - was part of a continuing spiral of attacks and reprisals that, two years after the Israeli invasion, have made southern Lebanon a nightmare for occupied and occupiers alike. Each day in south Lebanon there are several attacks on Israeli soldiers or their Lebanese allies. And, every day, the Israelis respond with gunfire, raids on villages, jailings and actions that wreak havoc on the economy, all of which further alienate the population.

Moving to broaden his appeal, Walter F. Mondale has enlisted Senator Gary Hart and the Rev. Jesse Jackson to stump for his candidacy and is preparing to draw some of their staff members into his campaign organization, Mondale aides say. After what the Presidential nominee called ''the most successful, meaningful, purposeful, united'' Democratic National Convention in recent history, Mr. Mondale's strategists prepared for him to begin politicking before the Labor Day kickoff for the general election campaign. Start in South Is Possible ''You'll see some activity in August,'' said Jim Johnson, the Mondale campaign chairman. ''We're working to arrange for the kickoff of the campaign to be in the South.''

WASHINGTON THEY loved it when Walter F. Mondale said he would raise taxes if elected President. They talked with glee about how the Democratic nominee had ''snubbed'' the South in picking his running mate. They belittled his efforts to expropriate the Republican themes of family, community, work and love of country. In spite of all their attempts to guard themselves against overconfidence, gloating prevails among President Reagan's re-election advisers. It does not seem to have been diminished by the unity celebration the Democrats staged at their national convention in San Francisco last week.

''The United States Army cannot be sustained in combat for any extended period of time.''

A comprehensive Congressional survey has concluded that the military's readiness to fight is declining and that American forces could not sustain combat against the Soviet Union or many lesser powers. A 376-page report drawn from the 18- month inquiry appeared to be the most sweeping public indictment of readiness in the armed forces since the issue was raised by members of Congress, mostly Democrats, in hearings on the military budget last winter. ''The United States Army cannot be sustained in combat for any extended period of time,'' the report said. It questioned the Navy's ability ''to sustain full combat air and surface operations for more than a week's time.'' And the Air Force, the investigators concluded, ''is not capable of conducting sustained conventional war operations against the Soviets.''

LOS ANGELES OS ANGELES and environs, which have given us Disneyland, Hollywood, Rodeo Drive, the transplanted Dodgers and a right turn on red, are about to present the greatest show ever on this part of earth - the Games of the XXIII Olympiad. For 16 days, starting Saturday, more than 8,000 athletes from 141 nations will offer a sporting festival that will be seen on worldwide television by an audience estimated at more than 2 billion. They will compete in 27 sports, including 2 demonstration sports - baseball and tennis. All those figures are records for this quadrennial spectacular. The logistics are staggering. The results, start lists and other information will be disseminated via 56 million photocopies. Hungry athletes and officials will eat 60,000 meals a day prepared by 135 chefs whose refrigerators will include 7,180 dozen eggs and 45,323 pounds of T-bone steak. Headaches and other ailments will be treated at polyclinics stocked with 65,620 pain-reliever tablets, 20,000 tongue depressors and 300 cans of baby powder.

THE return of the elderly from Florida has been described as a countertrend - a reverse flow of the retirees who 15 or 20 years ago left to settle in a warmer climate. Its impact has been noted in a number of northern states, and its effects are also being felt now in the county. These retirees are now part of the population called the ''old old'' - individuals in their 80's or 90's who are often alone, frail and without a family support system in their retirement community. At the offices of the Westchester Jewish Community Services in Hartsdale, Rosalyn Sabia, a social-work supervisor for the agency, described the increased demand for services that the agency has experienced. ''I get at least five calls a week,'' she said, ''and there are four other people who take calls as I do, so we get no less than 20 calls a week from a relative, a child. The call starts with: 'My mother is in Miami or Fort Lauderdale . . .' '' What Mrs. Sabia and her colleagues generally hear next is that some type of crisis has occurred and the adult child is thinking about bringing the elderly parent back to Westchester and needs help and advice.