A 23-year-old Boy Scout leader from Gaithersburg was arrested Tuesday night on sex offense charges involving an 11-year-old boy from his scout troop, Montgomery County police reported yesterday.

Michael May of 951 Clopper Road, leader of Boy Scout Troop 90 in Washington, was charged with second-and thire-degree sex offenses. He was released on a $15,000 unsecured bond, police said.

May was arrested in his Gaithersburg apartment, where police also confiscated magazines of a homosexual nature, and pornographic slides involving young boys.

For the past 18 months, May had been a scoutmaster at Troop 90, which is sponsored by Blessed Sacrament Roman Catholic Church on Western Avenue, according to Reed Clark, Troop 90 committee chairman. May had worked with Troop 90 for at least five years before becoming scoutmaster. according to Monsignor Joseph Corbett, pastor of Blessed Sacrament Church.

May is employed as a plumber's helper with Viking Plumbing and Heating in Rockville.

Clark described May as "strictly a scouting type... well-liked, quiet, very seldom lost his temper." He said he was one of the persons who recommended May for the scoutmaster position since May had a "good family background" and had done a "commendable job" in his earlier work with the scouts.

Rudy Flythe, executive director of the National Capital Area Council of Boy Scouts, said scout leaders are required to fill out a registration form for the position and their names are checked against a list containing the names of persons active in the scouts who have had criminal charges placed against them.

Flythe said this is the third incident in seven years in which allegations of sexual misconduct have been made against a troop leader in the Washington area. But in only one of the prior cases was a scout leader dismissed.

A second degree sexual offense involves committing a sex act with someone 14 years old or younger, by a person four or more years older than the victim. A third degree sex offense involves sexual contact with someone 14 or younger by a person four or more years older, police said.