A tiny fraction of the hoped-for millions have signed up for insurance under President Barack Obama's signature healthcare law, the government said on Wednesday, highlighting the scale of problems bedeviling Obama's biggest domestic policy achievement.

The law also confronted its most threatening legislative challenge since enactment in 2010, with Democratic Senator Jeff Merkley agreeing to co-sponsor a bill reopening the law in order to stem a wave of insurance cancellations.

Like four of the five other Democrats behind the measure, Merkley, who represents Oregon, is up for re-election in 2014. A similar bill is being sponsored by Republicans in the House of Representatives.

The proposals would let Americans hold on to coverage for the time being that is otherwise barred as substandard by the new law. That could curtail the number of young and healthy people purchasing policies through Obamacare insurance exchanges, threatening the program's financial viability.

Acknowledging deep concern about that possibility, White House Press Secretary Jay Carney said on Wednesday the Democratic president was rushing his own "fix" for the cancellation problem, which was caused by the provisions of the law.

"You can expect a decision from him and an announcement sooner rather than later," Carney said at his daily briefing.

Obama had promised repeatedly that Americans who liked their health insurance could keep it when the Affordable Care Act took effect on October 1. But several million people have received cancellation notices.

Until now, Obama's biggest legislative worry came from Republicans, who control the House but have been unable to dent Obamacare for lack of support from any Democrats, who control the Senate.

That balance, which has protected Obamacare from repeated attacks, is clearly changing. Even the title of the bill sponsored by the six Senate Democrats - "Keeping the Affordable Care Act Promise" - implied a rebuke to Obama.

BOTCHED ROLLOUT

House and Senate Democrats alike are increasingly concerned that the botched rollout of the law known as Obamacare could become a political liability for the party during the 2014 congressional elections.

On Thursday, White House officials will meet with Democratic senators, who want the White House to regain the upper hand.

While the low figure of 106,000 enrollments released on Wednesday was expected because of website technical failures, they showed how far the White House has to go to build an individual market of millions of consumers in 2014 to keep the healthcare program financially viable.

Obama's top technology officer stopped short on Wednesday of promising the website would be fixed by the end of the month, a deadline set by the administration.

"The team is working really hard to hit that goal and that's what I'm able to say right now," Todd Park, chief technology officer at the White House, told a congressional oversight hearing.

Fewer than 27,000 people signed up for private health insurance plans through the federal marketplace in October, the U.S. Department of Health and Human Services said. About 79,391 signed up through state-based exchanges.

One positive figure came from California, which embraced the healthcare reform policy early on and is considered one of the most crucial states for the enrollment effort. The state-un marketplace reported it had seen more than 59,000 individuals select health insurance plans from October 1 through Tuesday.

The pace of sign-ups has picked up in California in November - 29,000 have selected plans this month, already nearing the total of 30,830 reported in October.

The national enrollment figure for private plans amounts to 1.5 percent of a forecast 7 million people who were expected to sign up by the time enrollment wraps up at the end of March.

"The marketplace is working. People are enrolling," Health and Human Services Secretary Kathleen Sebelius said, blaming the website woes for the low numbers.

The Obama administration had said it expected a trickle of enrollments in October because of the error-ridden HealthCare.gov website used for signing people up in 36 states.

The government said 396,261 people were deemed eligible for the government's Medicaid program or the Children's Health Insurance Program for the poor.

Caroline Pearson, vice president at research and consulting firm Avalere Health, said the low number of sign-ups in private plans could force the government to extend the enrollment period.

"You've effectively shortened the open enrollment period, and I think this could lead to them lengthening the enrollment period on the back end," Pearson said.

So far, the administration has resisted calls for a longer enrollment period than established under the 2010 Patient Protection and Affordable Care Act.

POLL: DEMOCRATS HURT

Despite Obamacare's problems, Reuters/Ipsos daily tracking polls suggest that the president's approval rating, while at a low point, has not declined significantly since the rollout began.

Obama's approval rating was at 40.5 percent on Wednesday, the tracking polls indicated, while 52 percent of Americans disapproved of the job he is doing - figures that are essentially unchanged from October 1.

It has become clear, however, that the debacle has damaged Americans' confidence that Democrats have the better plan on healthcare. A year ago, when Obama was elected to his second four-year term, nearly 43 percent of Americans said Democrats had the better plan on healthcare, while 27 percent said Republicans did.

This week, only 31 percent of Americans favored Democrats on healthcare. But Obamacare's problems also seem to have dimmed Americans' support of Republicans on the issue: Just 17.4 percent now see Republicans as better on healthcare.

Nearly 1 million people have successfully checked whether they are eligible for government subsidies toward the new insurance, but have not selected a plan, officials said.

The sign-up figures reflect people who have picked a new insurance plan but may not have paid their premiums yet. Sebelius said enrollment should grow substantially over the next few months as the website improves.