April 29, 1982

EVER since car makers hit on the notion of the annual model change, planned obsolescence has been a standard marketing aid. The idea, of course, is to make the owner of last year's model feel stodgy and out of fashion so he'll rush out and buy the very latest. A kindred philosophy prevails in stereo. Each year a new generation of sound gear beckons from the shop windows, tempting the aficionados. But temptation should be distinguished from real need. In these economically wobbly times circumspect listeners are likely to ask themselves whether their sound systems really warrant replacement.

Here at South Commack, a large suburban high school where college has always been synonomous with sacrifice, more students than ever are planning to say no this year to elite private colleges and register instead at public institutions. Because of cutbacks in student aid and deepening economic uncertainty, close to three dozen seniors in this middle-income community have come to the conclusion that it will be financially impossible to attend Ivy League and other select colleges that have accepted them, according to the school's guidance office. Beverly Ballaro, for example, the salutatorian, who has spent an academic lifetime hoping to attend an Ivy League school, was recently accepted by Yale. Instead she will attend Rutgers, New Jersey's state university, which is considerably less costly.

the mansions in which interior designers display their talents - are a telling barometer of the design profession at a given moment. The Kips Bay Boys' Club Decorator Show House '82, one of the most prestigious, is no exception. As in years past, the Kips Bay Boys' Club invited a group of leading interior decorators to participate, with rooms assigned by lottery. It is the 10th annual event for this charitable organization, which helps disadvantaged children. But while past Kips Bay show houses tended to reflect new ideas and directions, this year's, which opened to the public yesterday, is more traditional.

A chart on Sunday gave an incorrect figure for the University of Central America's estimate of the number of civilians killed in El Salvador in 1981. The correct figure is 13,229.

A Federal judge ruled yesterday that New York State was failing to comply with reforms pledged in 1975 in care for the mentally retarded. He said he would name a special master at state expense to supervise the reform program. The judge, John R. Bartels of District Court in Brooklyn, charged that sanitation at the Staten Island Developmental Center in Willowbrook ''presents a serious health hazard'' to about 800 residents remaining under state care there. Life for them, he said, is ''sterile, dreary and one of enforced idleness.'' At least one patient, the judge said, ''choked to death as a result of being served an improper diet.'' Overall conditions, he said, had ''materially deteriorated'' since the State Legislature removed funds from a review panel in 1979.