A huge American-financed wastewater treatment plant in the desert city of Falluja, which United States troops assaulted twice to root out insurgents in 2004, was supposed to be the centerpiece of an effort to rebuild Iraq, a country smashed by war and neglect, and bring Western standards of sanitation.

Instead, the project, which has tripled in cost from original plans to $100 million and has fallen about three years behind schedule, has become an example of the failed and often oversold program to rebuild Iraq’s infrastructure with American dollars and skill.

The project was so poorly conceived that there is no reliable electricity to run pumps and purification tanks, and no money left to connect homes to the main sewer lines, which now run uselessly beneath Falluja’s streets, according to a report by federal investigators to be released Monday.

The report by the Special Inspector General for Iraq Reconstruction, an independent federal office led by Stuart W. Bowen Jr., stops short of saying that officials with the United States Army Corps of Engineers, which has primary responsibility for the project, or the American Embassy’s own reconstruction bureau, the Iraq Transition Assistance Office, deliberately withheld information on the problems.