Major health insurers, which decided early to support key aspects of President Barack Obama's health-care overhaul, are now picking through the Senate's version of the legislation and finding cause for concern.

Big insurers are still hoping to influence some language in the legislation before Congress sends it to the president. But one thing is clear: The initiative is poised to change their industry more than any other sector of the U.S. health-care system, with huge potential to disrupt profitability.

Cuts...