WASHINGTON — Days after formally announcing his candidacy for the 2012 Republican presidential nomination, Newt Gingrich on Sunday sharply criticized a plan by House Republicans that would drastically overhaul Medicare, the federal health care program for retirees.

Mr. Gingrich, the former speaker of the House who led a conservative resurgence in the 1990s, said the Republican Medicare plan was “too big a jump” for Americans and compared it to the health care overhaul championed by President Obama.

“I’m against Obamacare, which is imposing radical change, and I would be against a conservative imposing radical change,” Mr. Gingrich said on the NBC program “Meet the Press.”

“I don’t think right-wing social engineering is any more desirable than left-wing social engineering,” he said. “I don’t think imposing radical change from the right or the left is a very good way for a free society to operate.”