(Adds with background on the exchanges)
By Jeff Mason
WASHINGTON, Oct 19 (Reuters) - Roughly half a million Americans have applied for health insurance through new federal- and state-run exchanges under President Barack Obama's signature healthcare law, an administration official said on Saturday.
That figure comes as problems with the federal marketplace's entry portal serving 36 states, the website Healthcare.gov, have put a brake on the ability of consumers to shop for federally subsidized health coverage and drawn derision from Republicans, who oppose the law, popularly known as Obamacare.
The acknowledgement of the figure, late on a weekend evening, appeared to be a part of a ramped-up damage control effort by the White House.
The rollout of the legislation has been overshadowed by the website's glitches and frustrated Americans' inability to make it work.
"The website is unacceptable, and we are improving it, but the product is good and across the country people are getting access to affordable care starting January 1," an administration official said.
"We are going to work intensely for the next six months to make sure we meet the demand."
Another administration official said that among the roughly half a million applicants, more than half lived in states where the federal government was administering the health exchanges in full or in part.
Official figures from October activity are not due until next month.
Obama is holding a healthcare-themed event at the White House on Monday and will likely address the problems.
As Washington moves on from a 16-day government shutdown that concluded this week, Republicans are also turning up the heat on the administration to address the program's problems. Republicans in the House of Representatives triggered the government shutdown in a failed attempt to defund or delay Obamacare.
Republicans have criticized Health and Human Services Secretary Kathleen Sebelius for declining to appear before an oversight panel to discuss the issue next week.
Obama's Patient Protection and Affordable Care Act is expected to provide private health coverage to an estimated 7 million uninsured Americans through the new online marketplaces that opened for enrollment in all 50 states on Oct. 1.
But the Healthcare.gov website was hobbled by technical issues - including error messages, garbled text and delays loading pages - that administration officials blame partly on an unexpectedly high volume of 14.6 million visitors in its first several days of activity. (Additional reporting by David Morgan; Editing by Peter Cooney)