Fearing that health insurance premiums may shoot up in the next few years, Senate Democrats laid a foundation on Tuesday for federal regulation of rates, four weeks after President Obama signed a law intended to rein in soaring health costs. After a hearing on the issue, the chairman of the Senate health committee, Tom Harkin, Democrat of Iowa, said he intended to move this year on legislation that would “provide an important check on unjustified premiums.” Mr. Harkin praised a bill introduced by Senator Dianne Feinstein, Democrat of California, that would give the secretary of health and human services the...