SAN FRANCISCO - Wrapping up more than three years of work that cost the US government $2.3 billion, Bechtel Corp. is leaving Iraq with a subdued sense of accomplishment after suffering through a spree of violence that killed 52 workers.

The departure of the San Francisco-based engineering firm serves as another sobering reminder of how the carnage in Iraq has scrambled the United States' once-grand ambitions to rebuild the devastated country.

The US government hired Bechtel in April 2003, hoping the company behind manmade marvels like the Hoover Dam would be able to bring Iraq into the 21st century as it repaired much of the damage caused by the invasion that overthrew Saddam Hussein.

The daunting task required rebuilding roads and bridges, expanding the power grid, cleaning up the water supply and adding telephone lines.

Although some progress has been made, the efforts of Bechtel and other government contractors have been repeatedly beset by sabotage, corruption and lawlessness that made it difficult to retain workers frightened for their lives.

Bechtel said it completed all but two of the 99 projects on its Iraq to-do list, but at a horrible cost: 52 dead workers and another 49 wounded. At peak times, Bechtel employed more than 40,000 workers - mostly Iraqi subcontractors - on the various projects.

Most of the Bechtel workers were killed while off duty, said company spokesman Jonathan Marshall. It is among the greatest losses of life that Bechtel has suffered during any job in the company's 108-year history, possibly exceeded only by the company's Depression-era work on the Hoover Dam, Marshall said.

Bechtel has completed more than 22,000 projects in 140 countries, including perilous jobs like the Channel Tunnel that connects England to France.

Counting bodies was something that Bechtel never envisioned when the company went to Iraq. Within just a few months of arriving in Iraq, Bechtel had started to evacuate some of its workers from Baghdad to Amman, Jordan, for safety reasons.

Despite the adversity, Bechtel said it finished all its jobs except a water treatment plant in Baghdad and a two-story children's hospital in Basra that had been championed by first lady Laura Bush.

The government suspended work on the hospital last summer amid rising security expenses that drove the project well above its original $50 million cost. Bechtel estimated it would have taken at least $98 million to finish the hospital.

Before the hospital was abandoned, Bechtel's onsite security manager was murdered, another manager resigned because of death threats and a senior engineer quit after his daughter was kidnapped. Another 23 workers employed by a subcontractor and a concrete supplier were murdered.

When the government first picked Bechtel for the Iraq work, the decision was blasted by some critics who believed the company benefited from its deep political connections, particularly to the Republican Party.

Bechtel's leadership at various times has included George Shultz, a former cabinet member in the Nixon and Reagan administrations, and Casper Weinberger, the Secretary of Defense in the Reagan administration. Other employees, including Bechtel CEO Riley Bechtel, have connections to the current Bush administration.

The company maintains it won the Iraq business through a competitive bidding process that recognized its vast expertise. The Iraq contracts represented a relatively small portion of Bechtel's revenue, which totaled $51.8 billion from 2003 through 2005. The privately held company does not disclose its profits.

Bechtel's exit comes as Kroll, the risk consulting and technology division of Marsh & McLennan Companies Inc., announced it would sell a subsidiary that provides security services in Iraq and Afghanistan.