WASHINGTON — Thousands of people with serious medical problems are in danger of losing coverage under President Barack Obama's health care overhaul because of cost overruns, state officials say.

At risk is the Pre-Existing Condition Insurance Plan, a transition program that's become a lifeline for the so-called "uninsurables" — people with serious medical conditions who can't get coverage elsewhere. The program helps bridge the gap for those people until next year, when under the new law insurance companies will be required to accept people regardless of their medical problems.

In a letter this week to Health and Human Services Secretary Kathleen Sebelius, state officials said they were "blindsided" and "very disappointed" by a federal proposal they contend would shift the risk for cost overruns to states in the waning days of the program. About 100,000 people are currently covered.