The flow of oil through the trans-Alaska pipeline was halted again yesterday, according to the Interior Department.

A department spokesman said it was not specifically known what prompted the shutdown but that a check valve apparently failed at mile 26, south of Prudhoe Bay, the northern terminus of the 800-mile pipeline.

The stoppage came just hours after House investigators reported that the explosion and fire that shut the pipeline this month were the result of the failure of pipeline workers to follow procedures they had practiced for 10 weeks.

The House Interior Committee investigators said the July 8 explosion that killed one worker was caused by allowing oil to go through a pumping unit that was being repaired at the time.

Oil rushed through an unsecured hatch into a pump building, where it ignited, the investigators said.

The Interior Department had found earlier that human error caused the incident near Fairbanks and that the pipeline was not damaged. The department allowed the oil flow through the 799-mile pipeline to resume Monday.

Maintenance procedures at the pipeline include written notification of repairs but, the report said, that procedure was not followed before the accident.

Timothy Gidden, staff director of the panel's subcommittee on investigations, said he had identified the persons responsible for the explosion but would not make their names public.

Repairs to the pump station will cost $20 million to $50 million and take six months to a year to complete, he said.

The investigators said the incident could have been avoided if pipeline workers had followed the required maintenance procedures. But they recommended that electronic sensors he installed to automatically indicate when repairs are being done.