The Obama administration's healthcare law faces another challenge: a public largely unaware of major changes that will roll out in the coming months. Research suggests that most low-income Americans who will become eligible for subsidized insurance have no idea what is coming. Part of the problem, experts say, is that people who will be affected do not realize the urgency. Policy decisions are being made now that will affect tens of millions of Americans, and the lack of public awareness could jeopardize a system that depends on having many people involved. Low enrollment could lead to higher premiums, health policy experts say. Hospitals worry that, without widespread participation, they will continue getting stuck with patients' unpaid medical bills.