NEW YORK (AP) _ The 2-month-old son of a part-time U.S. marshal was taken from his stroller on a city street by kidnappers who lured his mother out of her house with a phony telephone call, police said.

''We have no motive, no ransom demand, no witnesses, no nothing,'' said police Sgt. John Mack. The kidnappers of Stephen Gentile have not contacted the infant's family since he was taken shortly before noon Wednesday, he added.

The infant's father, John Gentile, retired from the Conrail police force in 1984 with a disability, and now works part-time as a guard for the marshal's office.

However, investigators expressed doubt that Gentile's work was linked to the kidnapping.

''His work in Conrail was routine police work,'' Mack said. ''His work with the marshal's service is minor.''

According to police, Lucrezia Gentile received a telephone call about 1 1/2 hours before the abduction from a woman who told her that her 7-year-old son, John, was ill at school.

Mrs. Gentile put Stephen in his stroller and started walking toward St. Ephram's School in Brooklyn, the sergeant said. Suddenly, two men in a black sedan pulled up and the passenger got out to ask for directions.

''The driver of the vehicle walked around the car, and grabbed the baby from the stroller,'' Mack said. As the mother screamed, the men fled.

''Other than ask directions, they didn't say a word,'' Mack said.

The distraught mother failed to get the car's make or license plate number, the detective said.

Investigators determined the call from the school was fake.

Meanwhile in Holbrook, Ariz., a 4-hour-old baby was found today after being kidnapped Wednesday night from a Prescott hospital. A woman who claimed to be a laboratory technician took the newborn from his mother's arms, authorities said.

A Holbrook police officer making a check of a parked car found the kidnapped infant. The baby also was the officer's godchild, police said.

Two people were arrested for investigation of kidnapping, police said.

''The baby was still wearing hospital garments,'' said Holbrook police Sgt. Stewart Bracke. ''The baby's fine.''

Lisa Gerwitz was told Wednesday night that her son had to be taken to the Yavapai Regional Medical Center's laboratory for tests, said Prescott police Sgt. Bill Clayton.

When Mrs. Gerwitz asked a nurse about 45 minutes later where her baby was, authorities realized the infant had been kidnapped, Clayton said.

Prescott is approximately 170 miles west of Holbrook.

Bracke said Officer Douglas Newton, who discovered the baby in backseat of the parked car, knew the kidnapped baby's parents from high school.