A 33-year-old Arlington construction worker has pleaded guilty to the Aug. 29 sexual assault of an 11-year-old Springfield girl as she was walking to West Springfield Elementary School.

Mark L. Hancock, who has five prior arrests dating back to 1967 for indecent exposure, burglary with intent to rape and assault with intent to rape, was on probation after a January 1984 conviction for indecent exposure at the time of the attack.

Hancock could receive up to 20 years in prison, and he faces 3 1/2 additional years as part of a suspended sentence for the January conviction. Sentencing was set for Dec. 14.

The guilty plea to aggravated sexual assault, entered Tuesday, was part of a plea bargaining agreement, in which a more serious abduction charge was dropped.

Judy Dugger, Hancock's attorney, successfully sought a psychiatric examination for her client before sentencing.

Dugger said her client recognizes that he needs long-term psychiatric treatment, and said she will seek "commitment . . . for a very long period of time."

Raymond F. Morrogh, the assistant prosecutor who handled the case, said that he will seek "straight penitentiary time" because of Hancock's history of sex offenses. "I think it's just important to keep him off the streets," Morrogh said.

Hancock, of 4217 S. Four Mile Run Dr., was working as a drywall installer at a construction site less than a mile from the school at the time of the assault, Morrogh said.

The attack came as the sixth grader was walking on a sidewalk. She was grabbed, thrown to the ground and sexually assaulted, but not raped. She screamed throughout the attack, police said, drawing the attention of neighbors. Her attacker fled.