Besieged President Obama heads to Boston

Even as the White House planned that defensive strategy, the administration was forced Tuesday to deflect the latest round of complaints about the health plan debut — this time that hundreds of thousands of Americans are receiving notices canceling coverage, mostly of bare-bones, individual health plans that do not meet new minimum standards.

Republicans in Congress cited the cancellations to contend that Obama broke his own promise in 2009 that Americans under his law could keep their existing insurance, if they liked it. The president’s promise ultimately did not square with the fine print of the 2010 act, which prohibits insurance plans that offer patchy, weak benefits beginning in 2014.

News of widespread cancellations spread as officials and a squad of private contractors labored behind the scenes to fix the faulty Affordable Care Act marketplace websites, which have prevented people from signing up for subsidized insurance.

“It appears more people have received cancellation notices this month than have enrolled in the exchanges,’’ said David Camp, Republican of Michigan and chairman of the House Ways and Means Committee, as he convened a hearing to consider the problems.

Obama continued to come under fire in Congress for not explaining who in the administration was responsible for the flawed launch of the marketplace, which is supposed to allow residents to sign up for mandatory coverage in 36 states that chose not to operate their own marketplace sites.

Citing debilitating technical problems in the websites, Republicans and some Democrats are demanding that Americans be given a reprieve from the March 31 requirement to obtain insurance.

Obama’s visit to Massachusetts — where 97 percent of state residents have health care coverage — will provide a counterpoint to expected news Wednesday out of Washington. Secretary of Health and Human Services Kathleen Sebelius will face a grilling before Congress for the first time since the digital marketplace flopped dramatically on Oct. 1.

In a preview of Sebelius’s testimony, Marilyn Tavenner, the director of the federal Centers for Medicare and Medicaid Services, who answers to Sebelius, issued the clearest administration apology to date on Tuesday before the House Ways and Means Committee.

“To the millions of Americans who’ve attempted to use HealthCare.gov to shop and enroll in health-care coverage, I want to apologize to you that the website has not worked as well as it should,’’ Tavenner said. “This initial experience has not lived up to our expectations, or the expectations of the American people, and it is not acceptable.”

The Massachusetts law shares the mandate that most people obtain insurance; subsidies for low-income individuals and families to purchase coverage; and an online marketplace featuring plans, offered by private insurance companies, that individuals and small businesses can purchase at group rates.

Officials pointed out that the Massachusetts plan got off to a slow start, with just 123 state residents signing up in its first month.

“They started out very slowly. It took them years to get where they are today,’’ Tavenner said.

The demands on the Massachusetts marketplace were much smaller than the demands on the new federal system. With only a fraction of individuals signing up, it was rolled out in several phases, depending on the size of subsidies residents would receive. The federal site was open to everyone at once, and the administration has said the flood of people seeking to sign up overwhelmed the system.

Congress still has not received a clear answer from the administration on what went wrong with the federal insurance marketplace, which is estimated to have cost about $500 million and was in its early planning in 2010, soon after the Affordable Care Act was passed.

“Three years should have been enough,’’ said Camp. “I suspect many of these glitches could have been avoided.’’

In addition to underestimating demand, contractors have told Congress that development of the complex system was poorly coordinated and insufficiently tested before going live.

White House officials have also touted the bipartisan nature of the Massachusetts law — it was passed by a Democratic legislature and signed by a Republican governor — to try to convince Republicans to help make the federal law work.

“It was in everyone’s interest to put politics aside and focus on making the health care system better for people throughout Massachusetts,’’ said David Simas, a top White House adviser.

The political environment also is different today. The law pushed by Obama received no Republican support when it passed in 2010.

“I think, at this point, senators from both parties can agree: HealthCare.gov is a rolling disaster,” Senate minority leader Mitch McConnell said in a Senate floor speech on Tuesday. “Every day seems to bring more near-comic calamity . . . . I mean, the only thing this website seems to be good at right now is creating punch lines for late-night comedians.”

Republicans in Congress seized on insurance plan cancellations in the individual market — which covers about 5 percent of Americans — to accuse Obama of breaking promises that people would be allowed to keep their coverage and their doctors if they liked them.

As the law was written, that presidential promise was heavily qualified. In the individual market, only plans that existed before March 2010 — when the Affordable Care Act passed — will have such lasting “grandfathered’’ status.

Plans that were modified since then will be required to meet the law’s new minimum standards, which include coverage of things like maternity care, mental health and substance abuse, preventative care, and prescription drugs.

The administration has estimated that 40 to 67 percent of plans would experience normal changes between 2010 and 2011 and lose grandfather status — meaning that, unless they are upgraded to meet the minimal coverage standards, they will no longer meet the law’s requirements starting in 2014.

The Massachusetts health law, like the federal law, has a “minimum credible coverage’’ standard for its health plans.

Tavenner suggested the trade-off of such moves for consumers is that many of them will now get subsidies for plans with better coverage on the new HealthCare.gov marketplace. Also, they cannot be denied coverage for preexisting conditions, or purchase coverage that does not cover certain preexisting conditions.

At a White House briefing, Obama spokesman Jay Carney said the 2010 law was written to eliminate substandard plans and reform markets.

The individual insurance market, he said, “has been like the wild West, it has been under-regulated, it is the place where Americans have most keenly felt the challenges imposed by the insurance system in this country.’’

Matt Viser and Tracy Jan of the Globe Staff contributed to this report. Christopher Rowland can be reached at crowland@globe.com.