WASHINGTON — A former adviser to the Obama administration on health policy made public statements in 2012 that undercut arguments it is now making in court about the government’s authority to subsidize insurance premiums.

The adviser, Jonathan Gruber, a professor of economics at the Massachusetts Institute of Technology, said at a conference in 2012 that consumers could not obtain insurance subsidies under the health care law if they lived in states that refused to establish their own insurance exchanges.

His comments, captured on videotape, contradict the argument now made in court by the administration, which says that Congress always intended for the subsidies to be available nationwide, in all states, regardless of whether they had a federal or state-run exchange.

The subsidies are widely seen as essential to the survival and success of the health care law, President Obama’s most significant legislative achievement, adopted in March 2010 without any Republican votes. More than six million people who bought insurance on the federal and state exchanges have qualified for subsidies, in the form of tax credits.