The staff of the Federal Trade Commission has proposed a ban on television commercials aimed at children "too young to understand the selling purpose" of advertising.

As tentatively proposed by the staff, all product advertising on programs whose audience are made up of a "significant proportion" of children under the age of eight would be prohibited.

Depending on how "significant proportion" is defined - a term purposely left open-ended - advertising on some Saturday morning kiddie shows could be eliminated altogether under the proposal.

The staff also proposed banning the television advertising of sugared products that pose "the most serious dental health risks" on programs directed at audience of children between 8 and 11 yers olg. In addition, the staff would require advertisers of other sugared foods aimed at children to contribute to a fund that would balance those ads with separate dental and nutritional messages.

The commission is scheduled to take up the staff proposals and a 340-page backup report formally for the first time at an open meeting on Tuesday. The commission is expected to follow the staff's recommendation to institute formal rule-making proceedings, including public hearings, to determine whether it should go forward with the proposals.

The FTC staff began its investigation of children's television advertising in response to petitions filed last year by Action for Children's Television and the Center for Science in the Public Interest, two nonprofit organizations.

Both petitions, directed at commericals for candy or snack foods with more than 10 percent of their calories from added sugar, suggested that such advertising is unfair and deceptive within the meaning of the Federal Trade Commission Act.

The FTC staff agreed, but went further. "It is both unfair and deceptive . . . to address televised advertising for any product to young children who are still too young to understand the selling purpose of or otherwise comprehend or evaluate, the advertising," they told the commission. There are legal precedents which hold that even adults - presumably less vulnerable than children - are not to be exposed to "disguised" or "hidden" advertising the staff report suggested.

Legal principles also protect children against serious and lasting consequences of their own mistakes and against adult exploitation, the report continued.

A ban would have to be implemented in such a way that protects child audience without unreasonably foreclosing the right of adults to receive otherwise protected commercial speech, the report acknowledged.

In suggesting that it is unfair to promote consumption of some sugared foods through TV ads because of the adverse dental and health consequences that may follow, the FTC staff told the commission to consider data suggesting that:

The average child between 2 and 11 years of age watches more television a year than time spent in the classroom, and sees about 20,000 commercials a year (about three hours of advertising a week).

Many young children do not understand that television advertising is not a form of programming.

More than half the television advertising addressed to children is for food, most of which contains large amounts of added sugar.

Consumption of sugar and sucrose-related foods by Americans - more than 126 pounds a year - has led to "pandemic" tooth decay.

The likehood that some Americans are eating so much sugar that are excluding from their diet other foods that contain essential nutrients, with children believed to be disproportionately represented in that group.

In responsed to the FTC staff proposals, Vincent T. Wasilewski, president of the National Association of Broadcasters, said the industry believes its "television code" which includes specific guidelines for toy, snack food and cereal advertising is the "viable mechanism" to monitor ads and set standards.

"The ultimate responsibility and decision to purchase products rests with parents," he said. "Governmental intervention, no matter how well intentioned, is a dangerous precedent and not the answer."

In contrast, Robert B. Choate, president of the Council on Children, Media and Merchandising who made headlines several years ago criticizing breakfast cereal advertising, criticized what he called the "narrowness" of the staff proposals.

He said the staff was preoccupied with candy and sweets and ignored advertising of over-the-counter drugs and other products during programs seen other than Saturday mornings. ". . . 90 per cent of children's television watching occurs during afternoons and evenings seven days a week . . ." Choate said.