March 24, 1985

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.