What was going on when I was born?

FROM the windows of his home above Centerport Harbor, Leonard T. Stevenson keeps watch on what happens below. Since he arrived here in 1948, the 73-year- old retired New York City police detective has seen the tide in the narrow harbor go in and out many times. Looking past the shoreline home of his friend, United States Representative Robert J. Mrazek, he has smiled at the sight of swimmers and boaters making use of the waterway and bristled at the sight of raucous behavior. He has sprung into action to stop illegal filling, unauthorized dredging and the pumping of sewage into the old Mill Pond from harborside restaurants that have come and gone. There has been much to see, both good and bad. But never, Mr. Stevenson said, has he seen the likes of Harvey Vengroff and Donald A. Pius. Mr. Stevenson and many of his neighbors in the tightly knit harbor community, bound together in a half-dozen property owners' associations, are up in arms over what they see as the growing commercialization of their harbor. They believe the trend started when the two men started buying harborside property about two years ago.

IN the 1960's, regional conventions of newspaper publishers were like reunions of old friends - social events in which the prosperous scions of long-held family businesses played golf, compared notes on union troubles and speculated about what their dailies might be worth. But those days are gone. Family-owned newspapers are a rarity in America today. When publishers get together now, they are not typically the proud owners of family enterprises. More likely, they are the well- paid executives of newspaper chains - or of even bigger communications empires. Newspapers, and the media in general, are in the throes of dramatic change. In the march from family ownership to chains and to communications conglomerates, the industry is generating mega-mergers that rival in size the giant mergers of other industries. In this evolution, last week marked a watershed.

Concerned about reports of increasing drug use in sports, top United States Olympic officials say they want to conduct drug tests on American athletes at every major competition between this summer and the 1988 Games. Under a plan being prepared by the officials, athletes found to have used any banned drugs would be suspended from competition for one year following the first offense. A second offense would bring a four-year suspension, thus preventing such athletes from competing in the next Olympics. The drugs on the banned list - compiled by the International Olympic Committee - which have about 80 generic names and hundreds of brand and street names, include narcotics, stimulants and anabolic steroids. Some, such as cocaine, are not permitted in any amount, and others, such as caffeine, are permitted in certain amounts.

The Commerce Department's ''flash'' estimate for growth in the first quarter, released late last week, was weaker than expected - only 2.1 percent annual growth in the real gross national product, compared with 4.3 percent during last year's fourth quarter. Some economists, citing soaring imports and lackluster exports, are predicting a few more quarters of sluggish growth.

The police reported today that black activists had killed five fellow blacks they suspected of being Government stooges and that two other blacks were shot and killed by a black policeman. Five of the slayings were apparently in revenge for the police killing of 19 blacks Thursday in Langa township near the southern automotive center of Uitenhage. Many blacks in South Africa feel that blacks who work with the white authorities share responsibility for the authorities' actions. Thus, in the vengeful mood that followed the shootings Thursday, such figures would be seen as candidates for retribution. In the violence today, the homes of black policemen were set on fire.

Reagan Administration officials say they plan to encourage the development of private insurance for nursing home care for the elderly to help save money for Medicaid and Medicare. The Department of Health and Human Services commissioned a study of the subject, which concluded that there was a large potential market for such insurance. The study also said the use of private insurance could produce substantial savings for the Government. 'Significant Savings' Seen ''Long-term care insurance could have a significant impact on Medicaid expenditures'' by substituting private for public financing, it said, adding, ''Significant savings would occur even if only 20 percent of the elderly purchase the insurance.''

A 125-year-old residence just outside Atlantic City is serving as the stylistic and structural cornerstone of a small office and retail center now under construction in Absecon. The home, a three-story Victorian structure on the Old White Horse Pike near U.S. 9, is being restored, and it also is taking on a 6,000-square-foot, two-story addition that will be Victorian in style as well.

For most office tenants, basic space still means a floor, four walls, air-conditioning, heating and access to power and telephone lines. But the advent of computer-based office operations and telecommunications systems is quickly changing that.

Forty-six more savings and loan institutions reopened in Ohio today to a steady stream of customers who had access to their accounts for the first time since Gov. Richard F. Celeste ordered 71 state-chartered, privately insured thrift units closed March 15. State officials said a survey of thrift units open today found brisk but not unusually heavy business. They said more money was withdrawn than deposited but the level of withdrawals was not a cause for concern. ''It was excellent - beyond belief,'' said Robert B. McAllister, Ohio's superintendent of savings and loans. He said there were ''heavy runs'' on only two of the thrift institutions, which he did not name. He said, however, that these runs did not approach the magnitude of those last week when mounting concerns over insurance covering deposits at the thrift units led to a run on deposits at several of the institutions.

The United States, in a secret operation, today completed the evacuation of virtually all the Ethiopian Jews who were left in the Sudan after an Israeli-sponsored airlift was halted, Administration officials said. The operation was directed by the Central Intelligence Agency, and involved the State Department and the Air Force, the sources said. In a three-day period, 800 people were flown by C-130 Hercules transports to Israel, the officials said. Because of the sensitivity of the issue, the United States Government would not officially comment. Israel has also refused to discuss the matter and has imposed censorship on news dispatches related to it, saying that the lives of people involved were at risk.

ST. PETERSBURG, Fla. TAKE Vince Coleman: He is 23 years old, he is a switch- hitting outfielder and he can fly. Two years ago, he led the South Atlantic League by hitting .350; he broke every professional baseball record by stealing 145 bases, and he did it all even though he missed 31 games with an injury. Last year, he moved up to the highest level of the minor leagues and stole 101 bases, breaking the American Association record set four years earlier by Tim Raines. He didn't break it, he shattered it, by 24 bases.

AT the intersection of Third Avenue and 60th Street are the rear entrance to Bloomingdale's, several movie theaters, four brownstone tenements, a 16-story, off-white brick apartment building, and shops selling pizza, bagels, antiques and shoes. The commercial and architectural jumble is typical of this part of Third Avenue, which once was a back alley for the Upper East Side. But now developers of new buildings are billing Third Avenue as ''the crossroads of New York's energy and elegance'' and as a place to ''satisfy one's desire for ultimate convenience, unsurpassed prestige, architectural refinement.''