Leading Massachusetts health insurers and state regulators squared off in court Thursday in their dispute about acceptable health insurance premiums for a pivotal sector of the local economy: small-business owners.

The insurers argued the state's decision last week to reject nearly all of their proposed 2010 premium increases will cause "destabilizing" losses for them. The state said the insurers fundamentally misunderstand both the rate rejection and the way to resolve their dispute.

During a two-hour hearing in Suffolk Superior Court, an attorney for Blue Cross Blue Shield of Massachusetts and five members of the Massachusetts Association of Health Plans asked Judge Stephen Neel to issue a temporary injunction overruling the state's decision.

Attorney Dean Richlin also asked that the companies be allowed to collect the new premiums they had proposed be effective April 1 while a trial is held on the matter.

He said that requiring them to collect premiums at April 2009 rates, as he contended the state has ordered them to do, was "grossly unsound" and would create losses of more than $100 million in the next eight months.

"These are losses that will quickly mount up, and for some number of companies, the immediate losses will be destabilizing," Richlin said.