Federal copyright regulators are opening the door for new exceptions to a controversial copyright law that has landed one publisher in court and a Russian programmer in jail.

The United States Copyright Office is launching a rare round of public comment on rules that bar people from breaking through digital copy-protection technology on works such as music, movies, software or electronic books. Regulators aren't looking to change the law, but they are looking for public suggestions on what kinds of activity should be legalized in spite of the rules.

This is only the second time in the controversial law's five-year history that the public has been able to pitch in with suggestions for exceptions. Critics of the law say they will use the opportunity to draw wider public attention to the way its restrictions can affect ordinary people.

"Outside the copyright community, most people don't know this exists," said Fred von Lohmann, a staff attorney with the Electronic Frontier Foundation, a digital civil liberties group. "We're already planning to submit comments and organize comments by others. We're hoping that by the time the December deadline rolls around, a lot more people will be aware of this."

The portion of copyright law coming under the public microscope is the so-called anti-circumvention clause of the Digital Millennium Copyright Act, which bars people from circumventing "technological measure that effectively controls access to a work," as well as creating or distributing tools to do the same.

That law has been used by Hollywood in attempts to keep the DeCSS software program, which can be used in the process of copying DVDs, off the Web. It was the trigger for the FBI's arrest of Dmitry Sklyarov, a Russian programmer who had helped create technology that could crack Adobe Systems' e-book protections.

Free-speech advocates have challenged the constitutionality of the law, and the last round of public comments on the anti-circumvention clause three years ago drew an avalanche of comments from critics.

However, the copyright office says it has only a very limited scope to define exceptions to the law. In the last round, it carved out just two activities that could be exempted from the law. People could break through encryption on lists of Web sites blocked by Web filtering programs and could break protection on software or other "literary works" in cases where the copy control was obsolete or interfering with the functioning of the program, the office said.

This time around, the office is again asking for specific examples of cases where the law's restrictions cause "actual instances of verifiable problems occurring in the marketplace." Inconvenience or "theoretical critiques" are not enough, the office warned.

Von Lohmann cited several examples of types of activity that might merit exemption, including the "clean flicks" practice in which people delete scenes deemed objectionable from Hollywood movies and rent these movies to parents or other concerned viewers.

Public comments are due to the Copyright Office by Dec. 18.