KAJAKI, Afghanistan – In the approaching twilight of its war in Afghanistan, the U.S. is forging ahead with a giant infrastructure project long criticized as too costly in both blood and money.

It's a $500 million effort to refurbish the massive Kajaki dam and hydro-electric power system with an extensive network of power lines and transmission substations. It is supposed to bring electricity to 332,000 people in southern Afghanistan, increase crop yields and build up a cohort of trained Afghan laborers in a region badly in need of them.

But completion, which originally was envisaged for 2005, now is projected for some time in 2015, the year after most combat troops will have left the country. And there are some crucial ifs: