Lawmakers around the country are pushing for online registries, like those used for sex offenders, to track the whereabouts of people convicted of a wide variety of crimes, from arson and drunken driving to methamphetamine manufacturing and animal abuse.

State senators in Illinois are considering a law to create the nation’s first registry for first-degree murderers. In Maine, legislators are debating an online registry of drunken drivers. And proposals to register animal abusers have been put forward in several states; one such registry, in Suffolk County on Long Island, N.Y., will become operational next week.

Under a canine version of Megan’s Law, Virginia even registers dangerous dogs, including Elvis, a cat-killing collie in Roanoke whose bad acts are among those listed on the state’s database.

Advocates for online registries, many of them searchable by the public, argue that people have a right to know about potentially dangerous offenders in their midst and that the benefit of alerting parents, neighbors and others in a community outweighs any privacy concerns.

But as the registries proliferate, so do questions about their value. Critics say that while the registries are attractive to politicians who want to appear tough on crime, they often do little more than spread fear and encourage vigilantism. The monitoring systems cost money at a time when recession-strapped states can ill afford the extra expense, the critics say, and their effectiveness is dubious: Sex offender registries, for example, have had little success in reducing repeat crimes, studies suggest.

Wayne Logan, a professor at Florida State University College of Law and the author of a recent book on registration and notification laws, likens the registries to "legislative catnip."

"You’d be hard pressed to find a more politically popular movement in recent years," he said. "Whether it’s actually good public policy is a distinct and independent question from whether it’s politically popular and makes us feel good."

Logan noted that once passed, the laws were difficult to remove because politicians did not want to seem to diminish the suffering of victims. Instead, they are added "like Christmas ornaments on a tree, year after year."

The New York State Senate voted 57-4 Tuesday for a violent offenders registry. In Illinois, the murderers registry bill passed the House in April by a 97-1 vote. The legislation is now before the Senate.

Rep. Monique Davis, the lone member of the Illinois House to oppose the law, said that although she favored the state’s sex offender registry, "I just don’t think that a murderer registry is of much value to anyone except those getting paid to set it up."

She noted that the recidivism rate for murder was very low to begin with and that the state, facing a deficit of more than $4 billion, could not afford the cost of another registry.

But voting against such a measure, she said, is "very difficult to do, because sometimes the public perceives you as being soft on crime."

Rep. Dennis Reboletti, the main sponsor of the House bill, said that it "would allow not only law enforcement, but also the community to know who resides here, who our family members are associating with and who our children are dating."

"These are people who are lying in wait," Reboletti said in a phone interview. "It’s cold. It’s calculated. It’s planned over time. And it’s one of the most evil things that somebody can do on this earth."

The inspiration for the murderers’ registry, as for many such laws, was a high-profile crime, the 1998 murder of Andrea Will, an 18-year-old freshman at Eastern Illinois University who was strangled by her ex-boyfriend, Justin Boulay. Convicted before Illinois adopted a truth-in-sentencing law, Boulay was paroled from prison after serving half of a 24-year sentence, a turn of events that Will’s mother, Patricia Rosenberg, said she saw as "a slap in the face." She was even angrier when Boulay promptly moved to Hawaii to join the medical school professor he had married while in prison.

"I felt like I had to do something because I never felt justice was served," Rosenberg said in a recent phone interview.

She consulted with Reboletti on the idea for the legislation, known as Andrea’s Law. The law would require registration for 10 years after the offender is released from prison. It would affect 300 to 500 convicted first-degree murderers on parole in Illinois, Reboletti said, and 3,000 more who at some point will be released from prison.

A spokesman for the Illinois State Police, which would establish and maintain the registry, said the cost would depend on whether it could be built onto the state’s existing registries for sex offenders and child murderers, as some legislators have proposed, or would have to be created from scratch.

In Maine, concerns about cost have also been raised about the registry for drunken drivers. State Rep. Gary Plummer, a Republican, said establishing any new registry was "prohibitively expensive."

"I haven’t even gotten to the point of considering is it fair to put people on this type of registry, when we don’t have the resources" to do it, he said of the drunken driver bill, adding that he had also opposed proposals for arsonist and animal abuser registries as too costly.

Perhaps the biggest question about criminal registries is how effective they are in preventing offenders from committing future crimes.

Jill Levenson, an associate professor of psychology at Lynn University in Florida, who has written extensively about sex offender registries, has noted that Department of Justice figures suggest that only 13 percent of new sex crimes are committed by known sex offenders, and that such crimes are at least six times more likely to be committed by other types of offenders who do not appear on any sex offender registry.

Only a handful of studies have so far examined the effect of registry and notification laws for sex offenders on recidivism, Levenson said, but "so far, the vast majority of those studies do not show a decrease in repeat sex offenses that can be attributed to sex offender registry or notification."

Murderers have among the lowest rates of recidivism. Only about 1.2 percent of convicted murderers go on to commit another murder within three years of their release; roughly 35 percent commit other types of crimes within the same time period.

But in Rosenberg’s view, if even one murder is prevented by notifying the public it is worth it.

"Would it be more plausible if you thought they would commit four, five, six, seven murders?" she asked. "I think any life, one life, is worth saving."