That site says students can determine their legal residence, but advises them to consider certain questions. “Are you claimed as a dependent on your parents’ income tax return?” the site asks. “If you are, then their address is probably your legal residence.”

The site also tells students to check whether their coverage under their parents’ health or automobile insurance, or their scholarship, will be affected by changing their residence.

Civil rights lawyers say these guidelines are problematic and could infringe on students’ rights.

“What the state Board of Elections has on its Web site, to me, sounds like it is discouraging students from registering at their school address,” said Jon Greenbaum, director of the Voting Rights Project at the Lawyers’ Committee for Civil Rights Under Law.

Indeed, the Montgomery County registrar, E. Randall Wertz, said several students had canceled their local registration over their worry about the possible consequences. Mr. Wertz said he had issued the release to try to dispel confusion and explain what he believed to be the consequences of choosing a college address as a primary residence.

“My understanding of state law has been that by declaring you’re voting here, you’re saying this is your primary residence, your domicile, and that while you can have many abodes or residences, you can only have one domicile,” Mr. Wertz said. “And if this is your primary residence, you have to register your vehicle here, charge your driver’s license to here and so on. That’s been the interpretation at state training sessions.”

Kevin Griffis, the Obama campaign’s Virginia spokesman, said the release appeared to be a good-faith effort to convey state guidelines, not a politically motivated effort to stop voting by students.

Mr. Wertz said the initial release had been written by an intern whom he asked to summarize the guidelines. Although the second release used the state’s precise language, he said, it still left room for confusion. In other counties, registrars have refused to accept dormitory addresses as residences. But so far, the state has not set clear standards.