Medicaid rolls in the D.C. metro region will swell by hundreds of thousands under President Obama’s health care overhaul, hitting Virginia especially hard as the state scrambles to meet a vast new federal mandate.

The commonwealth, because its state health system is relatively modest, is expecting to take on between 275,000 and 400,000 new enrollees in the federal low-income health program after the expansion takes effect in 2014, with estimates varying depending on the predicted speed of economic recovery, said Dr. Bill Hazel, Virginia secretary of health and human resources.