He also stressed that the law allows Americans to keep bare-bones plans created before the law was signed, as long as insurers did not change or cancel them.
"Remember, before the Affordable Care Act, these bad-apple insurers had free rein every single year to limit the care that you received, or used minor pre-existing conditions to jack up your premiums, or bill you into bankruptcy," Obama said.
(Read more: Why Obamacare could raise your premiums at work)
America's Health Insurance Plans, the national trade group for health insurers, said the law requires coverage beyond what many people choose to purchase currently.
"Health plans want to keep customers," said group spokesman Robert Zirkelbach in a statement. In notices to customers about changes to their policies, he said, health plans were educating consumers about their options and helping them enroll in coverage "that's right for them."
'Broken health care system'
The law is the most sweeping new social program since the creation of Medicare and Medicaid in the 1960s.
It is intended to move the United States closer to the goal of universal care by using market-based mechanisms to deliver affordable insurance to less affluent families that have been priced out by decades of rising health care costs.
(Read more: Obamacare fixes need years: Cleveland Clinic CEO)
Obama said he would not allow the country to return to the previous system, which gave insurers wide latitude to refuse coverage to consumers that they did not deem profitable.
"I don't think we should go back to the daily cruelties and indignities and constant insecurity of a broken health care system," he said.
Technical woes, however, have prevented millions of Americans from exploring those options through the government's HealthCare.gov portal since it was unveiled.
On Capitol Hill, Obama's top health official called the debut a "debacle" as she sought to assure skeptical lawmakers at a congressional hearing that the administration would eventually get the portal to work smoothly.
HealthCare.gov was down over the course of the four-hour hearing.