A Brooklyn priest charged with a series of sexual abuse counts that could have landed him in prison for up to 25 years and required him to register with the state as a sexual offender managed to evade that fate by pleading guilty to a lesser crime of endangering the welfare of a child.

“People register when they’re convicted of a sex offense,” not when they are charged with one, the head of the Brooklyn district attorney’s sex crimes unit, Rhonnie Jaus, said.

The Reverend Joseph Byrns, a 63-year-old Brooklyn Catholic priest on administrative leave, was initially charged with two counts of sexual conduct against a child and 20 counts of sexual abuse for allegedly abusing a boy six times in a church rectory between 2000 and 2002, Ms. Jaus said. After a jury was unable to reach a verdict, Mr. Byrns pleaded guilty Monday to endangering the welfare of a child. He was sentenced to three years’ probation and is required to attend a Brooklyn sexual offender treatment program.

Such a stroke of good fortune is not the norm, Ms. Jaus said. “Most sex offenders do plead guilty to sex offenses” and therefore must register, she said.

In the priest’s case, she said, prosecutors struck the best deal they could considering the circumstances. The case was from long ago, it boiled down to the teenage victim’s word against the priest’s, and the victim had a history of arrests.

Endangering the welfare of a child is not a registerable offense, but it “should be” Ms. Jaus said.

Federal law mandates that convicted sex offenders register with local law enforcement. Megan’s Law – named after Megan Kanka, who at 7 was raped and murdered by a twice convicted child molester in New Jersey – varies from state to state, but allows officials to provide information to the public about offenders.

New York’s version of the law, the Sex Offender Registration Act, went into effect January 21, 1996. Governor Pataki signed amendments to the lengths of registration into law last week. Level 3, or high-risk, offenders are required to register for life; Level 2, or moderate-risk, offenders register for 30 years, and Level 1, or low-risk, offenders are in the registry for 20 years. Levels 1 and 2 can petition the court for relief from registering after a period of time.

The state’s Division of Criminal Justice Services, the sex offender repository, posts a subdirectory of high-risk offenders on its Web site – including the convicted offender’s name, home address, crime of conviction, and mug shot.

As of January 17, the registry contained 22,322 names, according to the criminal justice services Web site. Of those, there are 1,167 offenders on the list in New York County, with 332 of them listed as high-risk.

The registry helps to contain sexual offenders, the executive director of the New York City Alliance Against Sexual Assault, Harriet Lessel, said. However, she said, “the registry alone can’t be the whole strategy.” The Alliance is an advocacy organization that focuses on sexual violence issues.

A convicted sexual offender, Wayne Bowers, said, “In the long run, I don’t think it’s that effective.”

Bowers was convicted of two counts of indecent liberties with a minor in Hesston, Kan., for sexually abusing some boys he coached. He was imprisoned from 1989 to 1994. Exempt from the registry because of the date of his crime, Bowers has kept himself in check with years of therapy and by running the Sex Abuse Treatment Alliance in Lansing, Mich., a national organization promoting treatment for sex offenders.

The director of criminal justice services, Chauncey Parker, said there are some problems with the registry. One, he said, is that the subdirectory provides information only about Level 3 offenders. Information about Level 1 and 2 offenders can be obtained via telephone so long as the offender’s driver’s license number, Social Security number, date of birth, or exact address are known. This structure “undermines the purpose of having the sex offender registry to begin with,” Mr. Parker said.