A federal health official is expected to decide within days whether to expand an aid program for anyone sickened by World Trade Center dust to cover cancer, a move that would be cheered by many former ground zero workers, but could also prove costly and come at the expense of people with ailments more conclusively linked to 9/11's toxic fallout.

An advisory committee recommended in March that the government open up the $4.3 billion program to people with cancers in 14 different broad categories, including nearly all of the most common forms of the disease.

To date, there is little hard evidence of unusual cancer rates among people exposed to the soot that fell on lower Manhattan after the attacks. But the panel, made up of occupational health specialists, toxicologists, union officials and health advocates, said there were enough carcinogens present at the site to create a plausible risk.