Nearly half of a recent sample of school-age youngsters were left home alone at least occasionally, if not regularly, and many risked danger by improperly answering the phone or a knock on the door.

The Child Welfare League of America surveyed 447 children in kindergarten through third grade who live in urban, rural and suburban areas. In its November-December issue of Child Welfare, the league found that 42 percent of the children were left unsupervised at least occasionally, if not regularly."It was apparent that as children got older, parents were more and more willing to leave them without supervision," the authors said.

The percentage of "latchkey" children left alone occasionally or regularly in kindergarten was 28 percent; in first grade, 37 percent; in second grade, 45 percent; and in third grade, 77 percent.

"These figures far exceed any previously published estimates," the authors said.

The Child Welfare survey also found that urban children were far more frequently left unattended occasionally or regularly than rural and suburban children.

Parents said in interviews with the authors they were "doing the best they could" and felt they had no alternative.

While suburban parents were less likely to leave their children unsupervised, they were considerably more likely to leave them unattended for the occasional trip to the grocery store - 3 percent regularly vs. 35 percent occasionally.

In another part of the survey, parents of 16 children were asked to prearrange a 15-minute block of time when their children normally would be home alone. Children's responses were monitored when a telephone caller asked to speak with their mother and when a delivery person knocked on the door.

Only two of the 16 children performed appropriately on the telephone simulation. The optimum response was that their mother could not come to the phone and that they would like to take a message. At no point should the child give his or her name.

None of the children handled the package delivery portion effectively, with 13 opening the door and taking the package. The optimum response was for the child to go to the door, ask who is there without opening the door, and then ask the deliveryman to leave the package by the door.