PORTSMOUTH, N.H.  Fans and foes of President Obama’s push to overhaul health care descended on a local high school here on Tuesday to challenge him and hear him fight back against the criticisms  some outlandish  that have slowed the legislation’s progress.

“Parasites!” yelled the protesters on the right side of the school driveway.

“Ignorants!” yelled the protesters on the left side.

While apparently failing to convert the people outside who protested from the right side of the driveway, Mr. Obama sought to reassure the people gathered inside the school gymnasium that a health care overhaul does not mean that Americans will lose coverage or surrender treatment decisions to the government.

“Where we do disagree, let’s disagree over things that are real, not these wild misrepresentations that bear no resemblance to anything that has actually been proposed,” Mr. Obama told the meeting, attended by about 1,800 people.