"While the Ryan plan took the savings, they did not plow any of the money back into strengthening Medicare benefits and in fact they used the money as part of their plan for additional tax cuts for the very wealthy," Van Hollen said on a conference call.
Medicare has moved front and center in the presidential race since Romney picked Ryan to be his running mate on Saturday.
Ryan has galvanized conservatives with his plan to gradually convert Medicare's fee-for-service approach into a system that relies on private insurers to keep costs down.
Under Ryan's plan, retirees would get a set amount of money each year to purchase health insurance on the private market or to pay for traditional Medicare.
The amount of the subsidy would grow at a slower rate than the projected rate of medical inflation. The nonpartisan Congressional Budget Office says that could force retirees to pay more out-of-pocket costs for their medical care.
The plan would only apply to people younger than 55.
Public reception of the plan has been mixed, with older voters most skeptical. Obama and his fellow Democrats charge that Ryan's approach would "end Medicare as we know it."
Romney and Ryan are banking on the fact that voters, who go to the polls Nov. 6, are also unenthusiastic about Obama's health law.
Obama's planned health savings would come largely through reduced payments to hospitals and insurers, and patient benefits would not be affected. The savings would be used to expand health coverage to 30 million lower-income Americans.