Democratic leaders of a House science subcommittee alleged yesterday that the Federal Emergency Management Agency manipulated scientific research into the potential danger posed by a toxic gas emitted in trailers still housing tens of thousands of survivors of hurricanes Katrina and Rita.

FEMA "ignored, hid and manipulated government research on the potential impact of long-term exposure to formaldehyde" on Katrina and Rita victims now living in the FEMA trailers, the congressmen wrote in a letter to Homeland Security Secretary Michael Chertoff, whose department includes FEMA.