Action for Children's Television, a nonprofit advocacy organization, yesterday asked the Reagan administration to ban television commercials that encourage children to make telephone calls for which their parents are charged.

ACT filed a complaint with the Federal Trade Commission asking the agency to determine that the commercials are "deceptive and unfair" and to prohibit such advertising.

Congressional and FTC staff sources have indicated that the agency is investigating the practice.

ACT objects to commercials shown during children's TV programs or otherwise "targeted" at children that urge them to make calls that cost anywhere from 15 cents to $2 each.

In Colorado, one commercial encouraged children to dial a toll number to "talk to the Muppets," while one in New Orleans offered kids the chance to "dial Santa Claus every day until Christmas," said Peggy Charren, president of ACT, based in Newton, Mass. The commercials are shown throughout the country and could cost consumers millions of dollars, she said.

Rep. Timothy E. Wirth (D-Colo.) asked the FTC in June to investigate the commercials, citing the Muppets ad as an example. The commercial included a small printed statement that the call carried an extra charge, but Wirth said most young children "would be unlikely to comprehend such a warning."

The commercials are unlike other ads aimed at children because a child can spend money instantly, without realizing it, Charren said. Parents cannot screen purchases the way they can when children react to cereal commercials or toy ads, she said.

The solution does not lie in prohibiting children from using the phone, she said. "Kids have to be taught to use the phone to call the fireman or mom or for other help in an emergency."

ACT's complaint asked the FTC to ban such ads. If the FTC will not go that far, it should "specify remedial action" that would require advertisers to contract with the telephone company to provide "clear notification in each bill" of charges related to such ads, and to free parents of any obligation to pay for calls they do not authorize, Charren said.

Wirth said the Muppets ad has been taken off the air but asked the FTC to determine if such advertising violates any federal laws or regulations. The FTC said it has responded to Wirth and has received ACT's complaint, but would not comment further.