But she acknowledged that the federal reforms will make it more difficult to keep costs in check.

"There is some pressure for very positive reasons," said Quattrocki, citing a ban on denying coverage for pre-existing conditions and permission for adults 26 and younger to remain on their parents' insurance. "All those consumer protections are great news for Marylanders, but at the same time can create pressure on the rates."

Even if plenty of healthy uninsured Marylanders flock to the exchange, there could be other problems, critics said.

"We're setting up a system where we're going to expand health coverage, but the question is, where will we get the providers?" said Del. Adelaide Eckardt, an Eastern Shore Republican and a registered nurse. "If you overload the existing providers, then you're sacrificing the quality of care."

State health officials acknowledged that they will need to be ready to respond to glitches likely to arise along the way.

"We've done everything we can," Brown said. "We've done a lot to minimize the risk, and we need to maintain flexibility to respond to any unforeseen consequences of the risk that may still exist."

This article has been updated to clarify the findings of the Society of Actuaries report.

Reuters news service contributed to this article.