WASHINGTON -- Tens of thousands of Americans who can't get health insurance because of pre-existing medical problems will be blocked from a program designed to help them after funding ran low.Obama administration officials said Friday that the state-based "high-risk pools" set up under the 2010 healthcare law will be closed to new applicants as soon as today and no later than March 2, depending on the state.However, they stressed that coverage for about 100,000 people now enrolled in high-risk pools won't be affected."We're being very careful stewards of the money that has been appropriated to us, and we wanted to balance our desire to maximize the number of people who can gain from this program while making sure people who are in the program have coverage," said Gary Cohen, director of the Center for Consumer Information and Insurance Oversight, part of the Health and Human Services Department."This was the most prudent step for us to take at this point in time."The program -- the Pre-existing Condition Insurance Plan -- was always intended as a temporary bridge for the uninsured.But it was supposed to last until 2014. At that point, the healthcare law will bar insurers from rejecting or otherwise discriminating against people who are already sick, enabling them to buy plans through the private market.