A Gaithersburg man, described by prosecutors as "among the most dangerous child sex offenders in Maryland," pleaded guilty yesterday to his third child sexual offense in the last nine years, an incident that occurred two weeks after he was released from prison for an earlier offense.

Tarren Dikes, 27, was charged with luring two brothers, 6 and 8, to a drainage tunnel near their home in the Montgomery Village area in November and attempting to molest them. Prosecutors said Dikes was prevented from molesting the boys because he was interrupted by their father, who had noticed that his sons were no longer playing in their yard.

"This is someone who clearly cannot help himself and clearly needs to be removed from society," said Montgomery County State's Attorney Douglas F. Gansler, who called Dikes's deeds "vile and disgusting."

Dikes had been seen in the neighborhood befriending young children even though he was under a court order that forbade him to have contact with any child, prosecutors said. In 1990, Dikes was convicted of a sex offense against an 8-year-old boy, and in 1995, he was convicted of molesting a 10-year-old boy.

Dikes was sentenced to probation with counseling after his first conviction. After his second offense, he was sentenced to 18 months in prison followed by probation. Both were in Montgomery County.

At the time of the most recent incident, on Nov. 23, 1998,Dikes was on Depo-Provera -- the chemical castration drug -- and was undergoing counseling, according to prosecutors.

Because the boys' father prevented Dikes from molesting them, his pleas were to two misdemeanor counts. Dikes,who is being held in the Montgomery County Detention Center, is to be sentenced Sept. 21.