CRANSTON — Three-and-a-half years after a judge found Anthony Tavares not guilty of murder by reason of insanity, he remains in a state mental hospital here.

But confinement, it seems, has not quelled his appetite for public affairs: last month, he registered to vote.

Tavares, a Democrat, may not get a chance to choose between Senators Hillary Rodham Clinton and Barack Obama in the state’s March 4 presidential primary, though.

Last night, the city’s Board of Canvassers took the first step toward purging him from the voter rolls.

At the root of the move is a determination that Tavares, who stabbed his social worker in the head with an eight-inch serrated knife in November 2001, is too mentally ill to cast a ballot.

“If Charlie Manson were incarcerated here in the state of Rhode Island, should we allow him to vote?” said Joseph A. DeLorenzo Jr., chairman of the board, after the three-member panel voted to hold a public hearing on dropping Tavares.

Advocates for the mentally ill, who say a moment of madness years ago has little to do with an individual’s ability to choose a candidate, argued that the panel is going too far.

“I think they’re just asking for a lawsuit, basically,” said Jennifer Mathis, deputy legal director for the Judge David L. Bazelon Center for Mental Health Law in Washington, D.C.

The decision on Tavares was not the board’s first pronouncement on the sticky subject of mental illness and voting.

In August, the three-member panel voted unanimously to remove William Sarmento and John A. Sarro, both found not guilty of murder by reason of insanity some 20 years ago, from the voting rolls.

That decision has been stayed, pending an appeal to the Rhode Island Board of Elections.

DeLorenzo insists that the board has no interest in curbing the rights of those with manageable mental illnesses: this is about the truly insane, he says.

But the Cranston cases underscore a broader, national debate over who, exactly, is fit to cast a ballot.

Advocates for the mentally ill argue that election officials should tread lightly when it comes to curbing a fundamental, constitutional right.

Just because a mentally ill person has been placed under guardianship or declared incapable of managing money does not mean he is incapable of voting for president, they maintain.

Only a court ruling specifically declaring that the individual is incompetent to cast a ballot will do, they say.

A federal court in Maine vindicated that argument in 2001, striking down a state constitutional provision that barred voting by people under guardianship.

Advocates also claimed a victory last fall, when New Jersey voters decided to remove old language from the state Constitution that declared “no idiot or insane person shall enjoy the right of suffrage.”

But there is hardly a consensus nationwide.

In 19 states, authorities must obtain court rulings that specify a mentally ill person is incompetent to vote before removing him from the rolls, according to the Bazelon Center.

But 19 others have broader bans on voting by people who are under guardianship or “non compos mentis,” Latin for “not master of one’s mind.”

Rhode Island is in the latter grouping, with a constitutional provision holding that “no person who has been lawfully adjudicated to be non compos mentis shall be permitted to vote.”

In Cranston, the Board of Canvassers ruled that Sarro and Sarmento had, indeed, been found non compos mentis when the courts declared them not guilty of murder by reason of insanity.

And because twice-annual evaluations by the courts have not resulted in the men’s release, the panel found, the insanity finding stands.

But Kate Bowden and Kate Sherlock, lawyers with the Rhode Island Disability Law Center who represented the pair, sharply rejected that interpretation.

They argued the courts have made limited findings: ruling simply that Sarro, who slashed a man’s throat in a bar in 1981 and Sarmento, who admitted to murdering two boys in 1987, were insane at the time of the killings.

The courts, they noted, have made no determination about whether they are competent to vote.

The Disability Law Center filed notices of appeal with the state Board of Elections three days after the ruling.

And Robert Kando, executive director of the board, says he is awaiting some final paperwork from the center before scheduling a hearing.

The hearing, though, may not be the last to come before the panel: Bowden, who has represented Tavares on other matters, said she plans to take up his voting fight, too.

dscharfe@projo.com