More than half the American adult population feels that watching television is the cause of serious problems for children.

Strikingly, however, the people who express the most concern are either childless or parents whose children have passed the age at which most people would consider them impressionable, according to the findings of a national Washington Post poll. Parents of children under the age of 16 are concerned about the effects of TV on youngsters, of course -- but not quite as concerned as everyone else seems to be.

The Post poll dealt with three aspects of concern: TV content, the amount of time spent watching and the effect of TV advertising on children. The 1,693 people interviewed were asked whether they felt each aspect represented "a serious problem," "a minor problem," or whether it was "not a problem at all."

A total of 53 percent said they felt "the question of children seeing things they shouldn't see" was a serious problem; 32 percent felt it was a minor problem and 12 percent said it was not a problem. Among parents of children 15 or younger, 45 percent felt it was a serious problem; 38 percent said it was a minor problem and 15 percent said it was not a problem.

When asked how great a problem "TV keeping children away from doing other things they should be doing" was, 57 percent said they felt it was a serious problem, 28 percent a minor problem, and 12 percent said it was not a problem at all. Among parents of children 15 or younger, however, 49 percent felt it was a serious problem, 29 percent a minor problem, and 20 percent siad it was not a problem at all.

Somewhat less concern was expressed over "the effecxt of TV advertising on children." Thirty-eight percent of all those interviewed said it was a serious problem, 35 percent said it was a minor problem, and 22 percent said it was not a problem at all.

Again, parents of children 15 or younger seemed slightly less concerned. Among them, 34 percent said the effect of commercials on children was a serious problem; 39 percent said it was a minor problem, and 26 percent said it was not a problem at all.