September 20, 1982

New York City's population shifted as dramatically during the decade of the 1970's as at any time in the history of the city. That is the conclusion of demographers, planners and other city experts who have now had several months to study the first reports from the 1980 census. Markedly Fewer Children The figures provide a profile of a shrinking populace that nevertheless includes more old people and young adults, but markedly fewer children and teen-agers. The figures show what may have been the largest exodus of New Yorkers in the city's history. At the same time, they show a city that has become a magnet for a new wave of immigrants from Asia and Latin America.

Never mind that Labor Day has passed, that temperatures are just sneaking into the 70's, that department stores are filled with bulky sweaters, fur-lined gloves and argyle socks. David Elliot was oiled up and lying on the beach here today - he even went swimming - and though he certainly wasn't fighting for space to stretch out his towel, he wasn't alone either. ''As soon as Labor Day comes, most people put on winter clothes and think the beach is over,'' said Mr. Elliot, his manner showing clear contempt for this sort of thinking. ''Actually, now is the best time.''

''HUT-HUT, pass the potatoes.'' Scott Brunner smiled. It was a level-headed, intelligent smile, not overemotional, a smile in the manner he quarterbacks. When your father is a football coach and your mother a former college basketball player and women's field-hockey referee, dinner might be expected to sound like a locker room with pep talks between courses. ''It certainly wasn't like that,'' said Brunner, who will lead the Giants against the Green Bay Packers tonight in the first Monday night game at Giants Stadium. ''My father was a father. He wasn't a coach.'' ''Hut-hut, pass the salt.'' John Brunner laughed. ''Scott overcame it all,'' he said. If his son, the Giant quarterback, can be described as born and bred to play football, it wasn't because John Brunner, now the offensive backfield coach of the Detroit Lions, was in the business, or because the family sat around the table and talked of post patterns and weakside linebackers.

Dave Winfield sat in the clubhouse at County Stadium before today's game discussing the challenges remaining for the Yankees, a team already eliminated from this year's division race. He cited personal statistics, preparation for next season and performing the spoiler's role in the American League East pennant race. ''We're not even doing a good job of that,'' Winfield said of the final challenge. Then the Yankees went out and ran their losing streak to eight games with a 14-1 loss to the Milwaukee Brewers.

Twenty years after the Soviet Union touched off a major confrontation with the United States by stationing nuclear missiles in Cuba, six key Kennedy Administration officials say that the decisive military element in resolving the crisis was the availability of superior American conventional forces, not superior American nuclear forces. The former officials express their views and conclusions about what became known as the Cuban missile crisis of October 1962 in a two-page essay in the current issue of Time magazine. In a pointed allusion to the current debate about military posture, tactics and strategy, they write: ''The decisive military element in the resolution of the crisis was our clearly available and applicable superiority in conventional weapons within the area of the crisis. No one of us ever reviewed the nuclear balance for comfort in those hard weeks.