WASHINGTON - President Barack Obama thinks his health care law makes states an offer they can't refuse.Whether to expand Medicaid, the federal-state program for the poor and disabled, could be the most important decision facing governors and legislatures this year. The repercussions go beyond their budgets, directly affecting the well-being of residents and the finances of critical hospitals.Here's the offer:If states expand their Medicaid programs to cover millions of low-income people now left out, the federal government will pick up the full cost for the first three years and 90 percent over the long haul. About 21 million uninsured people, …