The full page ad shows a young child sitting with legs crossed, baseball hat tilted to the side, fist in the air.

"Kid Power!" screams the huge headline, "is coming to Boston."

"If you're selling, Charlie's mom is buying," the ad continues. "But you've got to sell Charlie first."

The ad, appearing in several national broadcast industry trade journals in August 1977, was placed by Boston television station WXNE-TV, Channel 25, a Christian Broadcasting Network station.

And with each line of copy in the ad, the message becomes clearer. "His allowance is only 50 cents a week, but his buying power is an American phenomenon. He's not only tight with his Mom, but he has a way with his Dad, his Grandma and Aunt Harriet, too.

"When Charlie sees something he likes, he usually gets it. Just ask General Mills, McDonalds or Mattel," the ad boasts.

Today, that advertisment is once again being widely circulated, but not by WXNE, any of the trade publications or the Christian Broadcasting Network.

It is being passed out by several consumer groups working to ban or severely cut back all television advertising aimed at children.

And it is just one of thousands of pages of testimony and exhibits submitted to the Federal Trade Commission, which is conducting an investigation -- called the "Kidvid" investigation -- into the effects of children's advertising.

The starting point for the FTC investigation is a report by the agency's staff, which has determined that it is inherently unfair and deceptive to address television advertising to children too young to understand or comprehend what is advertising and what is traditional programming.

For purposes of this proceeding, "too young" is defined as 8 or under.

The FTC staff also concluded that it is unfair and deceptive to promote, through television advertising, to children 12 and younger, the consumption of sugared foods associated with tooth decay, "because these commercials may take unfair advantage of the youngster's inability to comprehend the consequences of tooth decay or malnutrition."

The findings led the staff to propose a ban on the ads mentioned above, as well as a requirement that television advertising to children under 12 for other sugared products "be balanced by nutritional and health messages funded by the advertisers."

The consumer advocates claim that children cannot differentiate between commercial advertising and traditional programming, and therefore advertising aimed at children is unfair and misleading.

The broadcast, advertising, cereal and toy industries which are responsible for an estimated $600 million in children's advertising on TV, respond by saying that the job of teaching a child what is right and what is wrong is really the job of the parent, and that the government should stop trying to be a "national nanny."

But the issues surrounding the FTC probe have mushroomed into a major controversy raising serious questions about the First Amendment rights of advertisers, overregulation and the rights of children.

The controversy intensified a few months ago when a federal judge in Washington ruled that FTC Chairman Michael Pertschuk could not participate in the proceedings because he was biased in favor of some sort of ban, and had said so publicly several times. Pertschuk and the FTC are appealing that decision.

The FTC, under the auspices of hearing officer Morton Needleman, opened the public hearings portion of the investigation by listening to two weeks of testimony in San Francisco last month. Five more weeks of hearings are to open in Washington next month.

In two separate news conferences at the outset of those hearings, coalitions of consumer groups and industry representatives outlined their sides of the issue.

"Advertisements to any 3-, 4. or 5-year-olds can be nothing less than deceptive and fraudulent," said Consumers Union representative Harry Snyder.

Holding up the WXNE-TV "Kid Power" advertisement, Snyder said, "This ad tells you to get to Charlie's mom through Charlie. I submit that this ad is why we are here."

"It is time for corporation executives to worry about the child who has to say, 'Look ma, 10 cavities,' to worry about the parent who said to a child 'Kellogg's is lying to you,' and to worry even more about the parents who haven't yet learned to counter corporate irresponsibility," said Peggy Charren of Action for Children's Television (ACT), a Newton, Mass., nonprofit group. It first petitioned the FTC to study the children's advertising question nearly a decade ago.

And Jennifer Cross of San Francisco's Safe Food Institute said a claim by one industry spokesman that eating a sugary cereal, like Sugar Snacks, is comparable to eating an apple "is an insult to the apple."

For its part, the industry has waved the banner of the First Amendment, contending that its rights to free speech would be violated by the proposed FTC rules.

The Toy Manufacturers of America released a policy statement in San Francisco calling the FTC's involvement in the investigation "unnecessary" and citing overlapping jurisdictions with the Consumer Product Safety Commission, the Food and Drug Administration and the Federal Communications Commission.

And several industry spokesmen, led by a consortium of three advertising trade groups -- the Association of National Advertisers, the American Association of Advertising Agencies and the American Advertising Federation -- say there is no evidence of any psychological injury to children from television advertising.

"We are not dealing with little robots helplessly glued to the set, incapable of discerning between commercial and programs. We are interacting with capable, aware processors of information, so long as the inputs are simple enough to be grasped," said Fletcher C. Waller, vice president and marketing director of General Mills, in San Francisco testimony.

Another industry spokesman, advertising executive Seymour Banks, took that logic one step further in a subsequent interview, contending that television advertising helps a child to develop a healthy skepticism and evaluative skills.

"Children, like everyone else, must learn the marketplace," said Banks, a vice president of Leo Burnett U.S.A. advertising. "You learn by making judgments. Even if a child is deceived by an ad at age 4, what harm is done? He will grow out of it. He is in the process of learning to make his down decisions."

No matter who wins in the end, the fact that the issue of children's advertising has been raised so strongly has already had its effects on industry.

Shortly after the San Francisco hearings opened, ABC-TV President James E. Duffy told a meeting of his network's affiliates that the present 8 1/2 minutes of network advertising time per hour in Saturday and Sunday morning programming mostly aimed at children, would be cut back 20 percent in two stages beginning next January.

A few weeks later, ABC called for "separators" between children's advertising and programming -- brief spots informing the viewer that the programming has stopped and the advertising has begun, like "Superman will be back after these commercial messages," and, "And now back to Superman."

Although the rest of the industry accused ABC of "showboating," because separators have been used for many shows for years, Duffy denied the charges and said he was calling for industrywide standardization of separators.

As one FTC official, who asked not to be identified, said, "The ABC action is the kind of incremental victory we expected from this inquiry. We have hoped that there would be efforts by industry to regulate itself by placing some limitations on their children's advertising in an effort to head off government actions."