In their attempt to curtail repeat sexual predators, some members of the City Council are taking a cue from the reality television show “Survivor” and trying to vote them off the island. A bill co-sponsored by 14 council members would effectively exile ex-convicts classified as medium- and high-risk sex offenders from Manhattan.

The legislation, written by the council’s Republican leader, James Oddo of Staten Island, would bar Level 2 and Level 3 offenders from living, working, and “loitering” within a quarter-mile radius of schools, parks, playgrounds, and day-care centers. Violations would be punishable by up to six months in jail and a fine of up to $500.

An Oddo spokesman, Christopher DeCicco, said the minority leader has not commissioned a study to identify which sections of the city would lie outside proposed predator-free zones.

“That would be a big undertaking,” Mr. DeCicco said.

In a few hours, using a ruler and a street map, The New York Sun blocked off areas of Manhattan that would be rendered off-limits to offenders under Mr. Oddo’s bill.

South of Houston Street, nearly every square foot of Lower Manhattan, with the exception of a small sliver of land around the Fulton Fish Market, would apparently lie inside the predator-free zone. Convicted sex offenders might be allowed to live or work on several blocks in Midtown. But north of 54th Street, Manhattan could be completely off-limits. That is true even though the Sun’s crude survey, while it included parks and many public schools, did not seek to track areas around day-care centers, private playgrounds, or some private schools.

This week, the executive director of the New York Civil Liberties Union, Donna Lieberman, blasted Mr. Oddo’s proposal as a “knee-jerk response to a serious issue.”

She was not alone in expressing qualms over Mr. Oddo’s proposal. In a telephone interview, a prominent advocate for tougher laws on tracking sex offenders, Maureen Kanka, said she supports the establishment of buffer zones, in principle. But Ms. Kanka said she was concerned that Mr. Oddo’s bill, if enacted, might push sexual predators out of the city and into suburbs – such as Hamilton Township, N.J., where Ms. Kanka’s 7-year-old daughter, Megan, was raped and murdered in 1994 by a previously convicted offender, Jesse Timmendequas.

More than a dozen states have already enacted laws aimed at creating predator-free school zones, and last month, Binghamton, N.Y., passed a law nearly identical to Mr. Oddo’s proposal. But civil-liberties activists said the upstate city’s bill oversteps the bounds of municipal authority, and they said Mr. Oddo’s proposal would do so as well.

“The prescription of criminal punishments for sex offenders is up to the state Legislature,” Ms. Lieberman told the Sun.

Binghamton’s corporation counsel, Gregory Poland, said he has expressed concerns to lawmakers in his city that the buffer-zone legislation encroaches upon the state’s authority. And last week, on behalf of 15 sex offenders, Legal Services of Central New York filed a lawsuit challenging the constitutionality of Binghamton’s measure.

Council Member Tony Avella, a Democrat of Queens and a co-sponsor of the legislation, vehemently defended Mr. Oddo’s proposal.

“I don’t see why New York City shouldn’t have control of its own destiny,” Mr. Avella said. “I don’t see why it’s against the constitution for a society to protect itself.”

Some critics of the proposal said that in the long run, Mr. Oddo’s legislation might be counterproductive. A professor of human services at Florida’s Lynn University, Jill Levenson, said: “There’s no evidence that these policies actually work to decrease sex offender recidivism.” In a recent report co-authored by Ms. Levenson, a convicted offender is quoted as saying, “it is better for me not to have sexual contact with neighborhood kids – less chance of being recognized.”

At the same time, the director of the Center for the Treatment of Problem Sexual Behavior in Middletown, Conn., David D’Amora, warned that Mr. Oddo’s bill might actually increase recidivism. By limiting job opportunities for sexual offenders, Mr. D’Amora said, the proposed legislation would “create large groups of unemployed folks who all of a sudden have nothing to do” – except plan their next attack. Mr. D’Amora also noted that in the vast majority of sex offenses – approximately 85%, by most estimates – the predator knows the victim before the assault, and he said Mr. Oddo’s bill would do little to deter those attacks by relatives and caregivers.

But Mr. Oddo is unfazed.

“I’ve acknowledged that this bill isn’t a cure-all, and it may not even be half of a loaf,” the council member said. But he said his bill would ratchet up pressure on the state Assembly to pass legislation strengthening New York’s 10-year-old sex-offender registry, established under Megan’s Law.

In April, the state Senate approved a bill that, among other provisions, would require Level 3 offenders to wear electronic ankle bracelets, so that law enforcement authorities can track them using a global positioning system. With the clock running down on the 2005 session, the Assembly has yet to pass similar legislation.

In the city, according to the chairman of the council’s Committee on Public Safety, Peter Vallone Jr., a Democrat of Queens, Mr. Oddo’s will probably most likely will get a hearing this fall, after the September primaries.

“We need to do everything constitutionally possible to protect our kids,” Mr. Vallone, who is among the co-sponsors, said.