(WASHINGTON, DC) -- The Bush administration has appealed to the Supreme Court to reinstate a law that punishes Web site operators who expose children to dirty pictures and other inappropriate material.

The court has already sided with the government once this year in its war against online smut, ruling that Congress can require public libraries that receive federal funding to equip computers with anti-pornography filters.

In an appeal filed Monday, Solicitor General Theodore Olson said the filter technology alone is not enough. Children are "unprotected from the harmful effects of the enormous amount of pornography on the World Wide Web," he told justices.

The broader law at issue now requires that operators of commercial Internet sites use credit cards or some form of adults-only screening system to ensure children cannot see material deemed harmful to them. Operators could face fines and jail time for not complying.

Critics contend the law violates the rights of adults to see or buy what they want on the Internet.

Olson said the main target was commercial pornographers who use sexually explicit "teasers" to lure customers.

A Philadelphia-based appeals court has twice ruled that the 1998 law, known as the Child Online Protection Act, unconstitutionally restricts speech. The law has been on hold since it was challenged by the American Civil Liberties Union on behalf of artists, book stores and others who put information on the Web.

The Supreme Court has reviewed the law once. The justices were splintered in a 2002 ruling that sent the case back to the court in Philadelphia for more consideration of the First Amendment implications.

Jonathan Zittrain, a Harvard Law School professor who specializes in Internet law, said Tuesday that the high court will likely struggle again with what to do. "From the government's view, it can't hurt to appeal because it's essentially a roulette wheel," he said.

Zittrain predicted that the government will have a tougher time than it did persuading the high court to uphold the library filter law. The government argued in its filing that the cases are similar.

ACLU associate legal director Ann Beeson said the laws are very different because the 1998 statute involves criminal penalties for people who exercise free speech rights.

"I would have thought the Justice Department would have better things to do with its time than to defend what is clearly an unconstitutional law," she said.

The case is Ashcroft v. ACLU, 03-218.