A bill to let the state block excessive health insurance premiums is running into trouble in the Senate, where critics complain about its cost, its impact on large groups and the power it could give regulators with an ax to grind. Some of those arguments are specious; some of them are worth considering. But in any event, lawmakers shouldn't lose sight of the basic problem the bill would address: the inability of regulators to do anything but complain about unreasonable increases in premiums. The measure, AB 52 by Assemblyman Mike Feuer (D-Los Angeles), would give the Department of Insurance the same authority to modify or reject proposed increases in health insurance premiums as it has in automobile and homeowner's insurance. Similar power would be granted to the Department of Managed Health Care over the rates charged by HMOs.