Laura Ahearn, a certified social worker and mother of two daughters discovered more than two years after New York enacted the Sex Offender Registration Act of 1996 (Megan's Law), that the Suffolk County Police Department had stopped enforcing it.  In May 1998, Denny Chin, a Federal judge, ruled that Megan's Law could not be applied retroactively and the Suffolk County police mistakenly applied the injunction, meant for sex offenders who were on probation, on parole or incarcerated prior to the day the law took effect, to all convicted sex offenders.  Ms. Ahearn said, People were under the false impression that if a sex offender moved in next door, they would be notified.  She blames the lapse in enforcement on the misinterpretation of the recent judicial decision.  With the aid of local parents, community groups and state Assemblyman Steven Englebright, she helped bring about its reinstatement then formed Parents for Megan's Law.  The organization monitors sentencing for convicted sex offenders and maintains a Web site with information on registered sex offenders.