WASHINGTON – Senator Clinton came to the defense of beleaguered parents yesterday as she called for federal controls on violent and sexually explicit video games, which she said are corrupting America’s youth.

“Parents feel every day like they’re fighting this battle of all of these bad outside influences on their children with their hands tied behind their back,” Mrs. Clinton said. “I think we should do everything we can to make sure that parents have a defense against violent and graphic video games and other content that goes against the values they’re trying to instill in their children.”

Mrs. Clinton said she plans to propose legislation that would make it a federal misdemeanor to rent or sell a video game rated “adults only” or “mature” to anyone under 17. The offense would be punishable by a fine of up to $5,000, she said.

“The ability of children to access pornographic and outrageously violent material on so-called ‘M’-rated video games is spiraling out of control. It’s time to put the brakes on,” the senator said.

Game retailers immediately denounced Mrs. Clinton’s plan. “Senator Clinton must know that this proposal is unconstitutional. She’s a very good lawyer,” a spokesman for the Video Software Dealers Association, Sean Bersell, said. “Video games are covered by the First Amendment just as newspapers, books, and movies are.”

Mr. Bersell said local and state efforts to restrict the sale or rental of video games to minors have been uniformly rejected by the courts. “A rating of ‘M’ or even ‘AO’ is not a determination that the material is obscene or even obscene for minors,” he said. The industry spokesman said dealers have voluntary policies against selling or renting such games to young people.

A law professor who specializes in First Amendment issues said Mrs. Clinton’s proposal does not appear to meet legal muster. “It would be very likely unconstitutional,” Eugene Volokh of the University of California at Los Angeles, said. The Supreme Court has never approved restrictions on violent material, he noted.

Mr. Volokh also said enforcing the ratings decisions of a private group, the Entertainment Software Rating Board, would raise constitutional problems. “It’s nearly certain to lead to the criminalization of material that happens to have rubbed this particular unelectable, unaccountable group the wrong the way,” the professor said.

During a press conference yesterday, Mrs. Clinton singled out one popular but violent game, “Grand Theft Auto: San Andreas,” over reports that it contains sexually explicit scenes that can be unlocked after downloading special “mod” or modification software from the Internet. The game is rated “mature,” but almost certainly would have been rated “adults only” if the scenes were readily apparent.

“Disturbing material like that found in Grand Theft Auto or other games is stealing the innocence of our children,” Mrs. Clinton said. She asked the Federal Trade Commission to investigate how the sexual material was inserted in the game and to examine whether retailers are enforcing the industry’s voluntary ratings.

In response to a question, one backer of Mrs. Clinton’s proposal acknowledged that any teenager sophisticated enough to download the software “mod” could easily access vast troves of smut on the Web.

“Of course, you’re right. If you can download porn, this in a sense is not qualitatively different,” the president of Parents Action for Children, Norman Rosenberg, said.

Critics of the video game industry flanked Mrs. Clinton during her announcement and endorsed her proposals. “The federal government does have a role in challenging businesses when they overstep the bounds of civility and the law,” the director of public policy for the Family Violence Prevention Fund, Kiersten Stewart, said. “One can love the First Amendment, and I do, and still deplore Grand Theft Auto.”

The makers of Grand Theft Auto, Rockstar Games, noted in a statement that the game has won raves from reviewers. The firm offered no explanation for the sex scenes, but complained vaguely that some had misrepresented its best-selling game.

Mrs. Clinton’s attack on the video game industry evoked similar past crusades against the entertainment establishment, such as a campaign against explicit rock lyrics mounted by Tipper Gore, and efforts by Senator Lieberman, a Democrat of Connecticut, to reverse what he has termed the “coarsening” of American culture.

A former aide to Mr. Lieberman, Daniel Gerstein, said Mrs. Clinton’s move demonstrates that she understands that Democrats must show they are willing to stand up against perceived excesses in the entertainment industry.

However, Mr. Gerstein dismissed claims that Mrs. Clinton, who is considered a likely presidential contender in 2008, is acting solely for political reasons. “All the liberals who say this is pure political positioning by Hillary are full of it,” the political consultant said. “She’s been saying the same thing for 10 years. Now, it is a shrewd thing to do, but to say it’s all cynicism totally misunderstands her record and her motivation.”

While many stores sell or rent a wide variety of game, video, and music titles, Mrs. Clinton’s proposal made no mention of violent or sexually explicit videos or music CDs. By omitting videos and music, the senator avoided a direct confrontation with two industries that have powerful lobbies and provide generous campaign contributions to Democrats.

Asked if she favored similar restrictions on videos and music, Mrs. Clinton said, “I’m focused on video games.” She also said that there is mounting scientific evidence that video games, which tend to be highly interactive, alter the minds of young people in ways other media may not. “Video games have very specific impacts on children,” Mrs. Clinton said. “Watching violent video games actually affects the brains of children.”

Some opponents of federal regulation said Mrs. Clinton’s plan could have the perverse effect of causing game makers to withdraw from the ratings scheme. “If she was to introduce legislation threatening certain developers with stiff fines, why would they submit those games for ratings?” an analyst with a libertarian think tank, the Progress and Freedom Foundation, Adam Thierer, asked.