A 15-year-old Laurel youth was killed and his 18-year-old brother injured yesterday when "a pipe-type bomb" the brothers were making exploded in the basement of their family's home, Prince George's County police said.

The explosion occurred shortly before 4 p.m., and fire officials then evacuated neighbors of the home at 6609 Weaver Ct. as a fire department bomb squad searched the house. Police officials said a second bomb, presumably made by the brothers, was removed by the bomb squad and rendered harmless.

Paul J. Nicholas, 15, died of multiple injuries about 5:15 p.m. at the Greater Laurel-Beltsville Hospital. His brother, Mark, was in stable condition at Prince George's Doctors Hospital where he was being treated for a broken right arm and fragments still in his body from the blast, according to police. A police spokesman said one of the fingers on the youth's right hand was severed, and another was severely injured.

Homicide detectives said they believe the explosion was accidental, and other police spokesmen said they felt the construction of the bomb was motivated by an interest in experimentation with chemicals rather than by any destructive intention.

Authorities declined to disclose details of the contents or construction of the bomb, but did say that the explosive material was made from common and easily obtainable chemicals.

The investigation into the explosion is continuing, police said.

Neighbors said that the Nicholas family had lived on Weaver Court for about 10 years.