The consortium of state and local officials trying to finance a new regional hospital in Prince George’s County told Maryland lawmakers Wednesday that they expect to have a clearer picture of costs and benefits in the next 18 months.

At a briefing in Annapolis, Joshua M. Sharfstein, the state’s health and mental hygiene secretary, said the $600 million proposal “has tremendous potential and unique opportunities,” that will “move a long-standing problem and turn it in to a real highlight for the state.”

If the proposal moves forward as currently envisioned, a new hospital in the center of the county, along with a new, University of Maryland health sciences campus and a primary care outpatient network, could be operating in the next four to seven years.

Supporters of the proposed regional medical center, which would replace ailing, county-owned Prince George’s Hospital Center in Cheverly, portrayed the new system as a way to control rising health-care costs that ripple throughout the state, which is paying $15 million annually to keep the county’s hospital system afloat.

“If we don’t get a handle on this, we are going to pay for it one way or another,” said Prince George’s County Executive Rushern L. Baker III (D), one of the architects of the deal among the University of Maryland Medical System, the county, the state and Dimensions Healthcare, which operates the Cheverly hospital and other facilities for the county.

Some of the delegates and senators who had convened to discuss the proposal questioned the costs.

“At a time that every level of government is working to pay for basic services, it seems like a pretty big number,” said Sen. John C. Astle (D-Anne Arundel).

Baker said that doing nothing would ultimately cost more. Dimensions serves a large population of uninsured patients and has struggled to keep up with the expense.

“We recognize it is a big number. Clearly we have our challenges in our budget,” he said. But the ongoing county and state subsidies of $30 million, and paying for health care for uninsured residents who lack access to primary physicians, also is expensive, he said.

“This is actually driving up costs in Prince George’s County,” he said.

Carolyn Quattrocki, who heads Gov. Martin O’Malley’s office for health-care reform, acknowledged that funding the project will be challenging.

“I don’t mean to minimize the challenges ahead,” she said. “The financial ones will be the toughest of all.”