A Rockville man convicted last November in Montgomery County of sexually abusing his daughter over a period of 18 months allegedly kidnaped the 4-year-old child Wednesday from a day care center in Scranton, Pa., police said yesterday.

The FBI and police from Canada to Virginia are looking for John Wright Lourim Jr., 50, who they said may be armed and is considered dangerous.

Scranton police said yesterday that Lourim burst into his daughter's day care class at the Jewish Community Center waving what he said were custody papers. As two teachers tried to stop him from taking the child, he pushed them to the floor and then bumped his daughter's head against a doorjam as he fled the center, police said.

Authorities in Montgomery issued a bench warrant for Lourim after he failed on Jan. 28 to appear in Circuit Court to face sentencing for his conviction on one count of child abuse and one count of second-degree sexual offense of his daughter between January 1983 and September 1984. Lourim and his wife were separated more than three years ago when their daughter was 18 months old. The sexual abuse occurred during the daughter's visits with Lourim.

Wednesday's alleged kidnaping followed a bitter custody and visitation rights battle between Lourim and his wife that was waged in courtrooms in Fairfax County and in Lackawanna County, Pa., for nearly three years, according to court files.

Late yesterday Scranton police Sgt. Frank Roache said police have no clues as to where Lourim, who was driving a two-toned brown 1977 Monte Carlo, may have taken the girl. Court records said Lourim was unemployed.

"It's just like the ground opened up and swallowed them up -- there's no trace of him," the girl's 39-year-old mother said during a teary telephone interview yesterday from the Scranton home she shares with her parents. "She's got to be very, very scared and I'm anxious to get her home," she said, adding that her daughter was "deathly afraid" of John Lourim.

She described her daughter as having long dark blonde hair and hazel eyes and said she "likes to suck her right thumb when she's tired." The mother said the girl was wearing white leather sneakers with laces embossed with her name and flowers, blue jean overalls, a red and white plaid blouse edged in lace at the collar and cuffs and no coat.

John Lourim's father, who lives in a two-story yellow house in a quiet neighborhood in Hyattsville, said yesterday he had not seen his son since November. "I made damned sure I don't know anything about him -- I told him not to tell me," John Lourim Sr. said yesterday on his front porch.

From Montgomery County Circuit Court files that document Lourim's conviction by a jury Nov. 15, a picture emerges of a secretive man who frequently assumed identities of persons living and dead, who changed addresses and did not list his telephone numbers.

Lourim's lawyer in the child abuse case, John C. Maginnis, said yesterday he had not heard from his client since his conviction. "I have absolutely no idea where he is," Maginnis said, adding that the FBI had contacted him.

The Montgomery court records also show that the daughter suffered the physical and psychological scars of child abuse, according to letters submitted by psychiatrists and doctors who examined her.

"She's been going to counseling for an hour once a week for more than a year and she seemed like she was doing better," the girl's mother said. "She was adjusting to her new school and to her little classmates."