A new law included in the omnibus spending bill in the final days of the congressional session extends the definition of child pornography to include images that do not involve children at all, including movies that use adult actors to portray minors and even images created on computers.

The Child Pornography Prevention Act of 1996 has caused a furor among civil libertarians and constitutional law professors, many of whom sharply criticized the bill when it was first proposed by its sponsor, Sen. Orrin G. Hatch (R-Utah). The law took effect Monday when President Clinton signed the omnibus spending bill.

The new law outlaws "any visual depiction, including any photograph, film, video image or picture" that "is, or appears to be, of a minor engaging in sexually explicit conduct." The law lengthens maximum sentences for child sexual exploitation and child pornography, with penalties ranging from five years in prison to 30 years for repeat offenders.

As far as could be determined yesterday, no cases of the type of computer-generated child pornography described in the bill have been reported. However, advances in digital alteration of photography make the creation of such images possible.

"While federal law has failed to keep pace with technology, the purveyors of child pornography have been right on line with it," Hatch said in a statement.

Critics of the law said it would allow prosecution of legitimate works, potentially including such films as "Kids," and could cause a chilling effect on future productions based on such works as Vladimir Nabokov's "Lolita."

The bill also creates an exception to laws restricting newsroom searches. It would allow such searches in cases involving child pornography.

Though lawmakers are trying to protect children from the evils of child pornography, "what they're going to do is sweep up a great deal of constitutionally protected activity," said Daniel E. Katz, legislative counsel to the American Civil Liberties Union.

Neither obscenity nor child pornography is protected by the First Amendment's guarantee of freedom of speech. The legal definition of child pornography, however, is broader than the legal definition of obscenity because of the need to protect children from the exploitation and abuse that making child pornography entails. Child pornography has been defined to include "actual or simulated" sexual acts and "lascivious exhibition of the genitals or pubic area" of minors.

In prior cases, the Supreme Court stated that filmmakers could still use adults pretending to be minors in order to avoid exploiting children and breaking the law. But that course of action is expressly banned under the new law.

The statute is necessary because child pornography incites pedophiles to act out their fantasies and because they use such images to seduce children, said Bruce A. Taylor, president of the Fairfax-based National Law Center for Children and Families.

"The technology can make such a good counterfeit that you can't tell the difference between a Polaroid and a computer-generated image," said Taylor, an anti-pornography activist who advised Hatch's staff on the bill.

Yet such considerations have been considered and rejected by the Supreme Court in the past, said Eric M. Freedman, a Hofstra University Law School professor.

In the 1969 decision Brandenburg vs. Ohio, the court rejected the notion that the government could ban works that did not directly incite someone to commit an illegal act. And in the 1969 decision Stanley vs. Georgia, Justice Thurgood Marshall wrote that trying to "protect the individual's mind from the effects of obscenity" may be tantamount to asserting "that the state has the right to control the content of a person's thoughts. To some, this may be a noble purpose, but it is wholly inconsistent with the philosophy of the First Amendment."

"We have to be very cautious about restricting speech on the grounds that the recipient will abuse it," Freedman said. Noting that "people have been inspired to commit crimes because of the Bible," he said banning works because of what they might inspire others to do "is to reduce the level of the First Amendment to the level of the most perverted criminal among us."

Taylor said critics' concerns about the bill are exaggerated because it only applies to images peddled as pornography and not to legitimate works of art.

"We're not in the business of writing laws and enforcing laws just to put people in jail," he said. "We don't need to capture artists, or whatever. We need to capture pedophiles."

But Katz of the ACLU said that once a law is on the books, it can be abused by crusaders. "Nothing stops a zealous prosecutor from going after what a prosecutor doesn't like," he said.

Katz also noted that the chief defense against prosecution -- proof that the actors are of legal age -- does not apply if the material is proffered as child pornography, and does not apply to possession of such materials, only to production of them.

"This is an absolutely classic Washington phenomenon of everything that can't get passed during the session gets dumped into an omnibus bill at the end of the session," Freedman said. "Sen. Hatch knows perfectly well that this bill is unconstitutional." CAPTION: SEN. ORRIN G. HATCH