US President Barack Obama gestures as he delivers remarks on the Affordable Care Act, commonly known as Obamacare, at an Organizing for Action grassroots supporter event in Washington, Nov 4, 2013. [Photo/Agencies]

WASHINGTON - US President Barack Obama, defiant against mounting criticism of his troubled healthcare plan, vowed on Monday to press ahead with the rollout and asked supporters to help as the White House struggled to gain control of the debate over his signature achievement.

Obama went before 200 of the core activists who helped turn out the vote for him in his re-election a year ago, seeking their assistance to enroll people into the Affordable Care Act amid signs that early enrollment numbers will fall far short of expectations.

"I need your help to implement this law," he told leaders of the Organizing for Action group that grew out of his 2012 campaign. "I need your help to educate folks about this law."

Obama has come under fire for a website that has not worked properly since the system came online October 1 and for the fact that thousands of Americans are seeing their private insurance plans canceled despite his 2010 promise that under Obamacare, "if you like your healthcare plan, you'll be able to keep your healthcare plan".

The problems have contributed to a drop in his job approval rating to about 40 percent and given his Republican critics ammunition to use against a healthcare law they have fought bitterly since it was proposed during his first presidential campaign in 2008.

'GOING TO KEEP ON GOING'

Obama promised that the problems with the website will be fixed and vowed the healthcare law would not be stopped.

"When the unanticipated happens, we're just going to work on it, we're going to fix things that aren't working the way they should be and we're just going to keep on going," he said.

His administration has set a target of the end of November for HealthCare.gov to be operating smoothly. Aides on a conference call with reporters promised it would be much improved, a possible sign that all problems will not be worked out in time.

Obama called the website problems "inexcusable" and said he wants to address federal procurement rules for information technology.

"There are a whole range of things that we're going to need to do once we get this fixed to talk about federal procurement when it comes to IT and how that's organized," Obama told a smaller, invitation-only group who had a private question-and-answer session with him.

The Obama administration is scrambling to get people enrolled in the Obamacare system, with the first month's enrollment figures to be released in about 10 days and expected to be lower than anticipated.