WASHINGTON (AP) _ Children's TV advocates Sunday were outraged by President Reagan's veto of a bill to limit advertising during kids' shows, calling his action ''ideological child abuse'' and promising to revive the legislation next year.

Despite lopsided passage of the bill by Congress, Reagan pocket vetoed it Saturday night on the grounds that it would violate constitutional guarantees of free speech.

''Consistently this administration has put commercial considerations and ideological precepts ahead of children's interests,'' said Rep. Edward J. Markey, D-Mass., a coauthor of the bill.

''The president's actions represent a victory for the toy and cereal hucksters, but a major defeat for our nation's children,'' he said.

The bill would have reimposed advertising limits scrapped by the Federal Communications Commission four years ago under the theory that an open marketplace would best regulate commercials for children.

The measure also would have required TV broadcasters to provide educational and informational programming for children as a condition of license renewal.

It was approved on a voice vote in the Senate last month and by a margin of 328-78 in the House in June.

Reagan, however, said that while he supports efforts to improve the quality of children's programs, ''this bill simply cannot be reconciled with the freedom of expression secured by our Constitution.''

He said, ''the Constitution simply does not empower the federal government to oversee the programming decisions of broadcasters in the manner prescribed by this bill.''

Conditioning license renewals on programming decisions would violate the First Amendment and would ''inhibit broadcasters from offering innovative programs that do not fit neatly into regulatory categories and discourage the creation of programs that might not satisfy the tastes'' of FCC officials, Reagan said.

In addition, he said, the bill's limit on commercials ''may well undermine its stated purpose by discouraging commercial networks from financing quality children's programming.''

Children's television advocates had pushed for the bill because they said that under the FCC's deregulatory approach advertising during children's shows has increased and the quality of the programs has suffered.

''Killing a bill that would have encouraged terrific TV for children is another example of ideological child abuse in the Reagan administration,'' said Peggy Charren, president of the Cambridge, Mass.-based Action for Children's Television, which has worked 20 years for passage of the measure.

''The ultimate effect of the veto is that we will continue to have a broadcast industry that spends all its time figuring how to benefit from children instead of how to benefit children,'' she said.

Markey said he was certain Congress will pass the bill again next year.

The measure was a bipartisan compromise that had been stripped of proposals to outlaw shows, called ''program-length commercials'' by critics, that feature toy manufacturers' products and to require broadcasters to air an hour of educational programming per day.

The bill as passed would have limited advertising in children's shows to 10 1/2 minutes per hour on weekends and 12 minutes per hour on weekdays.

The final measure had the tacit support of the broadcasting industry after the National Association of Broadcasters lobbied effectively against the stronger versions of the bill.

Edward O. Fritts, president of the National Association of Broadcasters, said that ''while we recognize this legislation charted some new territory, we were willing to accept its outcome.''

''Under any circumstances, we are very sensitive to our responsibility to provide quality programming to children and we will continue to do so with or without legislation,'' he said.

The veto puts back on track an FCC inquiry into the commercialization of children's TV. The commission is considering whether it is necessary to impose advertising limits and regulate program-length commercials and interactive toys that respond to inaudible signals beamed through TV sets.

But lawmakers and children's TV advocates say they do not expect the current FCC to deviate from the deregulatory path over which it has moved throughout the Reagan administration.