SOMERSET — Level 2 and 3 sex offenders won’t be able to take out a library book, participate in any public events at a park or school, join other adults in a pickup softball game at any playground, or spend more than 15 minutes conducting business in the town offices under a proposal that will come before voters at Monday night’s Annual Town Meeting.

It’s also unlikely that offenders will be allowed to attend future town meetings after Monday night, even if they have lived in Somerset for years.

Under the proposal, listed as Article 39 on the agenda, they are allowed to enter a school or library to vote in an election, but a town meeting isn’t an election. The meetings are held at the high school, from which they are banned.

The idea for the bylaw comes from Selectman Lorne Lawless, who said similar measures have been ruled constitutional in other communities.

“This regulation has passed constitutional muster,” and it uses the best language from other communities where the rules have been upheld, Lawless said last night. “We feel it will pass [Monday night] and we feel it will protect the children. That’s it.”

He declined to discuss specific implications of the law.

“You have my statement,” he said.

But the American Civil Liberties Union of Massachusetts strongly opposes such laws. The organization says it can understand the desire to protect youngsters, but only 7 percent of sexual assaults against children are done by a stranger; relatives or acquaintances are responsible for 93 percent.

In addition, the data suggest “that these measures are not only ineffective, but may actually increase the likelihood of sex offenses,” according to the ACLU.

The Somerset proposal “is something we would consider challenging,” the legal director of the organization, John Reinstein, said yesterday. He estimated that about 20 such municipal bylaws have been passed in the commonwealth.

The ACLU is not challenging them right now, he said, because some bylaws haven’t been onerous enough or no sex offender has been willing to come forward and allow the ACLU to sue the city or town on his or her behalf.

“It’s not for a lack of interest [by the organization] in doing so,” Reinstein said

According to the Massachusetts Sex Offender Registry Board, Somerset has 16 Level 2 sex offenders, who have been categorized as having a moderate risk of re-offending and are considered dangerous enough that their whereabouts must be available to the public.

The state says the town has two Level 3 sex offenders, who are regarded as posing a substantial risk to public safety and are highly likely to engage in sex crimes again. (However, four individuals were identified as Level 3 offenders in notices posted in the town offices last night.)

If approved Monday night, the bylaw must still be OK’d by the attorney general. Town lawyer Clement Brown said the language proposed for Somerset is similar to what was approved by the attorney general within the past month.

The proposal, one of the last on the agenda, is designed to keep children, seniors and the mentally impaired out of harm’s way by banning people convicted of sex crimes from most public facilities, unless they have written permission to be there.

It also prohibits them from spending more than 15 minutes within 500 feet of the property lines of schools, libraries, daycare centers, parks, beaches, playgrounds, athletic fields, or facilities for the mentally impaired or for the elderly, which includes people over 55.

For example, offenders who wanted to attend a meeting of the selectmen or various boards and commissions could only be there for 15 minutes because those groups meet at the town offices, located between the Council on Aging offices at the old Pottersville School and the town library.

Similarly, an elderly offender would be banned from the Council on Aging offices without special permission, no matter when their offense occurred.

And the proposal would require offenders to move if they take up residence within 500 feet of those areas.

The bylaw will not force offenders — who must already register with the police — to move from the homes or apartments they live in now.

If they move within 500 feet of school property, for example, they will have 30 days to move. Every extra day they spend there will result in a $300 fine.

The ACLU says there are lots of reasons to oppose what the bylaw characterizes as the “safety precautions.”

A Dedham, Mass., bylaw put 76 percent of the town off limits to sex offenders, although the no-living zone is larger than Somerset’s and the no-loitering zone, which included all school bus stops (unlike the Somerset proposal) is smaller. The remaining 24 percent of town where the former offenders can live includes cemeteries and conservation land.

The bylaw would require Somerset to draft maps showing the restricted zones. The maps would be on file at the Police Department and town clerk’s office.

“Because residence restrictions often force offenders to live away from supportive family members and employment and treatment resources,” the ACLU says, “this lack of community support structures tends to make rehabilitation more difficult and relapse more likely.”

The organization asserts that such bylaws are unconstitutional “in that they impose an additional punishment long after the time of the offense.”

“There are, of course, alternatives to what amounts to a policy of banishment,” the ACLU says in a position paper. “Massachusetts already has a comprehensive sex offender registration requirement,” it says, and the parole system is getting better at supervising offenders, and programs for treating them can be effective.

“Residence restrictions add little to these existing approaches and may actually interfere with them,” the ACLU says.

gemery@projo.com