"I recognize that there's still a lot of folks in this town at least who are rooting for this law to fail," Mr. Obama said. "Some of them seem to think this law is about me. It's not — I already have really good health care."
He chided Republican lawmakers for "refighting these old battles," holding dozens of votes to repeal parts or all of the 2010 Affordable Care Act.
"Sometimes I just try to figure out why," Mr. Obama said to laughter from his invited guests. "Maybe they think it's good politics."
The president was joined by families who have benefited from the health care law provision that provides consumers with a refund if their insurance company doesn't spend a set percentage of premium dollars on medical care and improving health care quality, rather than administrative costs or overhead.
Mr. Obama was introduced by Morgan Theriot, a self-employed woman from Silver Spring, Md., who received a $267 refund check from her insurance company last summer after it didn't meet the requirement to spend at least 80 percent of her premium dollars on her health care.
"I'm curious — what do opponents of this law think that folks here today should do with the money they were reimbursed?" Mr. Obama asked. "Should they send it back to the insurance companies? Do they think that was a bad idea, to make sure that insurance companies are being held accountable?"
But Senate Minority Leader Mitch McConnell, Kentucky Republican, said the president isn't telling Americans the full story.
"What he won't say is that next year, Obamacare will impose a new sales tax on the purchase of health insurance that will cost Americans about $8 billion," Mr. McConnell said Thursday. "If the administration is concerned with saving people money on their health care, I have some advice for them. Work with us to repeal Obamacare and start over."
Speaker John A. Boehner, Ohio Republican, said the GOP will continue its efforts to repeal the law.
"The picture that the president paints of his health care law looks nothing like the reality facing struggling American families," Mr. Boehner said. "The law is costing American jobs; it's forcing people to give up health plans they like; and it's driving up the cost of care for families across America. In my home state, many Ohioans will pay nearly $200 more a month, on average, for individual plans. This law has to go."
For the law to work as its supporters envision, more young and healthy people need to sign up for insurance under the various health exchanges being set up in states. The audience at the White House included community groups who will be working at the grassroots level across the country to help enroll Americans in the new health insurance marketplaces this fall.
Mr. Obama's pitch came a day after the House voted to delay mandates in the federal health care law requiring individuals and large employers to have coverage, with dozens of Democrats joining Republicans in poking a symbolic hole in the president's signature achievement.
Thirty-five Democrats joined with House Republicans to give large businesses a one-year reprieve on the requirement to provide health insurance for full-time employees, helping pass that provision on a 264-161 vote.
The House also voted 251-174 to give individuals the same one-year break, with 22 Democratic lawmakers joining Republicans. The measures are certain to go nowhere in the Democrat-controlled Senate.
The president chuckled at Republican lawmakers for repeatedly voting to repeal provisions of the law.
"Yesterday, despite all the evidence that the law is working the way it was supposed to for middle-class Americans, Republicans in the House of Representatives voted for nearly the 40th time to dismantle it," he said. "We've got a lot of problems in this country, and there's a lot of work that Congress needs to do."
Mr. Obama said Americans are already seeing benefits from the law, including in New York, where officials this week said individuals buying insurance on the state-based health care exchange in 2014 will see their premiums drop by an average of 50 percent compared with last year's direct-pay individual rates.
The president's progressive allies launched a TV ad campaign timed to coincide with the president's message. Americans United for Change went on the air with a new TV ad, "Hands Off Obamacare," attempting to put the GOP on the defensive for trying to strip away provisions of the health law.
"Republicans want to take your benefits away and put insurance companies back in charge," says the announcer in the ad. "Obamacare is working. Tell Republicans — hands off Obamacare."
The administration announced July 2 that it was postponing for one year, until 2015, the law's requirement for employers with more than 50 workers to provide health insurance for all full-time employees.
Sharon Stiller, an employment law specialist at the New York firm of Abrams, Fensterman, said many of her employer-clients expect the law's definition of "part-time" employee to be changed. Currently the law defines a part-timer was any employee who works less than 30 hours per week.
"The word on the street is that there may be some changes with respect to the definition of 'part-time," Ms. Stiller said. "It's harder for employers to decide to do the necessary planning because they're not sure exactly what the final criterion will be."