DENVER (AP) _ A valve malfunction shut off oxygen to 19 critically ill newborns for up to two minutes last weekend and one infant died three days later, officials at Children's Hospital said.

''The relationship between the baby's death and the oxygen interruption is uncertain,'' hospital spokeswoman Julia Fitz-Randolph, adding that the cause of the infant's death Tuesday was difficult to determine because the child had multiple illnesses.

Hospital officials said Thursday that they are investigating the cause of Saturday's malfunction, in which an interior valve on a pipe leading from a main oxygen supply tank was closed, said hospital president Lua Blankenship.

An alarm system alerted hospital staff members to the oxygen shutoff.

Oxygen from backup tanks then was pumped into the babies' incubators in the hospital's Newborn Center, where critically ill infants from 1 day to 28 days old are treated. No infant was without fresh oxygen for more than two minutes at a time, Blankenship said.

Fitz-Randolph said a lock was installed on the valve ''to avoid future repetition of the problem.''