EIDFJORD, Norway (AP) _ A bus driver said his brakes failed on a steep road and he tried to stop the careening vehicle against a tunnel wall, but the bus crashed, killing 12 children and three adults, the Norwegian news agency NTB reported today.

The crash Monday outside Eidsfjord, 120 miles west of Oslo, was the worst bus accident in Norway since 1948.

Among the 15 fatalities, 12 were children from a Stockholm school on a week-long outing to the British Shetland Islands. All 19 of the other passengers were injured, police said. They said the Swedish bus was carrying 23 students, nine parents, a teacher and the driver.

Hans Jacob Berntsen, 46, of Bergen, Norway, was driving behind the bus and was the first at the scene, according to the Oslo daily Dagbladet.

''I talked to the injured driver. He said the brakes had failed and that he tried to stop the bus by letting it swerve along the tunnel walls,'' Berntsen was quoted as saying.

''He told me that he had urged the passengers to stay in the rear of the bus. That may have saved the lives of several of them,'' he said.

The bus rammed into a concrete wall near the end of the steep, curving Maaboedal Tunnel, about 60 miles from the city of Bergen, where the group was to board a ferry, according to the Stockholm daily Aftonbladet.

Survivors were evacuated by helicopter and six people were reported severely injured but out of danger, according to a doctor at Bergen's Haukeland Hospital.

Bernt F. Moe, chief constable in the Hardanger district where the crash occurred, said a crane was used to lift some of the bodies from the wreckage.

The 11- and 12-year-olds who died were from the Kvarnbacka Primary School in the Stockholm suburb of Kista. A teacher at the school told Aftonbladet the students had spent two years holding bazaars and saving money to finance the trip.

The tunnel, which has had no fatal accidents since it opened in 1986, is about 120 miles northwest of Oslo.

Swedish Radio said the bus was not licensed for commerical traffic and was rented or borrowed from a sports club. The driver was a police officer licensed to drive a bus, according to the Aftonbladet daily in Stockholm.

Norway's worst bus accident occurred on July 5, 1948, when 16 people were killed on a remote northern road.