Four media groups are seeking the "least restrictive" enforcement of a new law that limits the number of commercials during children's television programs, saying the statute infringes on free speech rights.

In a brief filed with the Federal Communications Commission, the groups contended that the Children's Television Act of 1990 violates the First Amendment by assigning to the federal government the role of "dictating a portion of the programming of privately owned television stations. ..."

The brief was filed Tuesday by the Radio-Television News Directors Association, whose membership includes news executives from the nation's broadcast industry; the Reporters Committee for Freedom of the Press, a journalists group that advocates First Amendment rights; the Media Institute, a Washington-based research organization; and the Society of Professional Journalists, which counts nearly 20,000 broadcast and print journalists among its members.

President Bush last October allowed the act to become law without his signature, saying he backed its goals but objected to provisions he believed would infringe on free speech rights. President Reagan previously vetoed two similar bills. In 1984, during Reagan's administration, content of children's programming was deregulated.

Advocacy groups criticized Bush for not signing the new statute, which they insisted would give the television industry an incentive to become a partner in the education of the nation's youth.

But the coalition of media groups said that there had been "no showing of need for the legislation" and that the FCC already had "determined that the market functions adequately to regulate the quantity and quality of children's television programming."

The commission must adopt and implement rules for enforcement of the act, which would limit commercials on children's television shows to 10 1/2 minutes for each hour of weekend programming and 12 minutes an hour on weekdays.

Also, the FCC must consider in its study of TV station license renewals how well the broadcasters are serving the educational and informational needs of children.

In their filing, the groups said that while they realized the FCC had a responsibility to enforce the law, "the commission should minimize this infringement on the First Amendment rights of information media by interpreting and enforcing the act in the least restrictive manner."