WASHINGTON — BP, running weeks behind schedule and tens of millions of dollars over budget trying to complete its troubled Macondo well in the Gulf of Mexico, took numerous shortcuts that contributed to the disastrous blowout and oil spill last year, federal investigators concluded in a report released Wednesday.

The central cause of the explosion aboard the Deepwater Horizon drilling rig was a failure of the cement at the base of the 18,000-foot-deep well that was supposed to contain oil and gas within the well bore. That failure led to a cascade of human and mechanical errors that allowed natural gas under tremendous pressure to shoot onto the drilling platform, causing an explosion and fire that killed 11 of the 126 crew members and caused an oil spill that took 87 days to get under control.

The two-part report, compiled by a joint task force of the Bureau of Ocean Energy Management, Regulation and Enforcement and the U.S. Coast Guard and covering more than 500 pages, is the most comprehensive to date on the April 2010 disaster. Its findings largely mirror those of other investigations, including the inquiry by the commission named by President Barack Obama to determine the causes. That panel issued its findings in January.

“The loss of life at the Macondo site on April 20, 2010, and the subsequent pollution of the Gulf of Mexico through the summer of 2010 were the result of poor risk management, last-minute changes to plans, failure to observe and respond to critical indicators, inadequate well control response and insufficient emergency bridge response training by companies and individutals responsible for drilling at the Macondo well and for the operation of the Deepwater Horizon,” the latest report said.

It concluded that BP, as the well’s owner, was ultimately responsible for the accident. But it also said that BP’s chief contractors, Transocean, which owned the mobile drilling rig, and Halliburton, which was responsible for the cementing operations, shared blame for many of the fatal mistakes.

The Justice Department is conducting a criminal investigation that could bring indictments and heavy fines.

David Uhlmann, a professor at the University of Michigan Law School and former chief of the Justice Department’s environmental crimes section, said the Justice Department almost certainly reviewed the findings of the study before it was released.

“Today’s report increases the likelihood that BP, Transocean and Halliburton will face criminal charges for their roles in causing the gulf oil spill,” Uhlmann said in an e-mail. “The Justice Department may have outside experts for both its criminal and civil cases, and it could develop additional information about the causes of the spill in those investigations, but it will be hard for the Department to distance itself from the findings of the Coast Guard and Boemre.”

The well blowout unleashed a spill of nearly 5 million barrels of oil, fouling the gulf and hundreds of miles of beaches, marshes and fish habitats and causing billions of dollars in damage.