WASHINGTON – The Pentagon’s official watchdog will investigate allegations by Halliburton water experts that their company endangered American troops in Iraq by failing to provide safe shower and laundry water.

The most serious allegation came from the company’s water treatment manager in the war zone whose internal report said troops and civilians in Iraq were left vulnerable to “mass sickness or death.”

A former Halliburton water expert who found contamination at the Ar Ramadi base a year ago said he was told by superiors not to advise the military or senior company officials of his discovery.

Senator Dorgan, a Democrat of North Dakota, who had asked for an investigation, released a letter yesterday confirming the audit from John Crane, the Pentagon’s assistant inspector general for communications and congressional liaison.

Gary Comerford, spokesman for the Defense Department’s inspector general, said the audit would be among the first two by the inspector general’s new office in Qatar.

The audit will “look at everything involved in this issue,” Mr. Comerford said.

Mr. Dorgan, who has held Democratic-only hearings on the water issue, said the risk to American forces in Iraq “should not include behavior by contractors who cut corners and whose incompetence fails to manage a program that is supposed to deliver safe water supplies.”

The internal company report, obtained by the Associated Press, was written last May by Wil Granger, the “Theatre Water Quality Manager” for Halliburton’s KBR subsidiary.

The report cited confusion between the military and the company over their water treatment responsibilities, a lack of training and the absence of records that might have provided warnings of contamination.

Despite the author’s management position with KBR, the company said parts of his report were incomplete and inaccurate. A company report four months later found no problems in the contractor’s stewardship of water supplies for American troops and civilians, and no incidence of illness, Halliburton said in a statement. The company has declined to make either report public.

Mr. Granger wrote of the discovery in March 2005 of contamination of laundry and shower water at Camp Ar Ramadi in Ramadi. At the time, the nonpotable water came directly from the Euphrates River.

“This event should be considered a ‘near miss’ as the consequences of these actions could have been very severe resulting in mass sickness or death,” Mr. Granger wrote.

The report said company water treatment units “had been on site for a considerable amount of time without assembly” due to resistance from a KBR foreman, who believed if they had been operating, “it would expose his weak knowledge base.”

Mr. Granger wrote that the problems were not confined to Ar Ramadi.

“Countrywide, all camps suffer to some extent from all or some of the deficiencies noted,” Mr. Granger wrote in the May 2005 report.

The AP reported this year on allegations from whistle-blowers about the Camp Ar Ramadi incident.

The water quality expert warned Halliburton the problems “will have to be dealt with at a very elevated level of management” to protect the health and safety of American personnel.

Halliburton said it has “worked closely with the Army to develop standards and take action to ensure that the water provided in Iraq is safe and of the highest quality possible.”

Halliburton was headed by Vice President Cheney for several years before he became George W. Bush’s running mate. Its KBR subsidiary, also known as Kellogg Brown & Root, works under contract to provide a number of services to the American military in Iraq, including providing water and purifying it.

The contaminated, nonchlorinated water at Ar Ramadi was discovered in March 2005 in a commode by Ben Carter, KBR’s water expert at the base.

In an interview, Mr. Carter said he re signed after KBR supervisors at the base “told me to stop e-mailing” company officials outside the base and warned that informing the military “was none of my concern.”

He said he threatened to sue if company officials did not let him be examined to determine whether he suffered medical problems from exposure to the contaminated water.

Mr. Granger’s report confirmed that KBR officials at Ar Ramadi tried to keep the contamination from senior company officials.

“The event that was submitted in a report to local camp management should have been classified as a recordable occurrence and communicated to senior management in a timely manner,” Mr. Granger wrote. “The primary awareness to this event came through threat of domestic litigation.”