The debate over whether to let states opt out of any government-run health insurance plan overlooks a key facet of the health-care measures being assembled in Congress: When Washington is done, the shape of any new health-care system is likely to be finalized in Lansing and Boise and Baton Rouge.

Besides the opt-out choice, proposed last week by Senate leaders, health-care legislation being drafted on Capitol Hill would delegate to state officials a multitude of momentous decisions, from what benefits are offered to low-income families to what hurdles to put in front of private insurance companies before they can raise premiums.

"The fact is that state programs are going to look different," said Judith Solomon, a senior fellow at the Center on Budget and Policy...