WASHINGTON — The leading American effort to capture carbon dioxide from coal plants has hit a stumbling block that could imperil the project and set back a promising technology for addressing global warming, people involved in the venture said.

...While the other major partners, Babcock & Wilcox and Air Liquide, could seek to buy the plant and convert it without Ameren, time is short. The federal government promised the project $1 billion, or roughly 80 percent of its costs, on the condition that the money be spent by the end of 2015.