Wonkblog's Sarah Kliff shares her "Kliff Notes" for President Obama's remarks defending his signature healthcare law. (Phoebe Connelly/In Play/The Washington Post)

Days before the launch of President Obama’s online health ­insurance marketplace, government officials and contractors tested a key part of the Web site to see whether it could handle tens of thousands of consumers at the same time. It crashed after a simulation in which just a few hundred people tried to log on simultaneously.

Despite the failed test, federal health officials plowed ahead.

When the Web site went live Oct. 1, it locked up shortly after midnight as about 2,000 users attempted to complete the first step, according to two people familiar with the project.

As new details emerged about early warning signs of serious deficiencies in HealthCare.gov, Obama on Monday gave a consumer-friendly defense of the health-care law, insisting that the problems many Americans have faced in trying to enroll in insurance plans will be fixed quickly.

“There’s no sugarcoating it: The Web site is too slow; people have been getting stuck during the application process,” he said at a White House event.

Calculator: How much will you pay for insurance?

At the same time, he admonished Republican critics of the federal insurance exchange, saying that “it is time to stop rooting for its failure.”

The president’s remarks reflected rising anxiety within his administration over the widening problems with the online enrollment process. “There’s no excuse for the problems,” he added, “and they are being fixed.”

Obama said government officials are “doing everything we can possibly do” to repair the site, including 24-hour work from “some of the best IT talent in the country.”

“No one is madder about the Web site than I am, which means it’s going to get fixed,” he added.

White House officials said Monday that the problems have not caused the administration to consider delaying the law’s individual mandate, which requires that most Americans have health insurance next year or pay a fine.

(Read more about the rollout of the new health-care law.)

A Washington Post-ABC News poll released Monday shows that a majority of Americans, 56 percent, believe that the Web site’s flaws reflect larger problems with the health-care law, an alarming figure for the administration. But support for the law is growing despite the enrollment issues, with 46 percent of Americans saying they support it now, compared with 42 percent who said so last month.

Congressional Republicans have called for the firing of Health and Human Services Secretary Kathleen Sebelius over the enrollment problems. House Republicans have been pressuring her to testify before the Energy and Commerce Committee on Thursday to answer questions about the health-care rollout. Sebelius, who is scheduled to be in Phoenix that day, agreed Monday night to appear on Oct. 30 instead.

Several companies working on HealthCare.gov have confirmed that they will send representatives to the hearing. They include two of the main contractors, CGI Federal and Quality Software Services Inc. (QSSI), a subsidiary of UnitedHealth Group, as well as Serco, which is handling paper applications, and Equifax, which is dealing with some of the income verification.

“We are now entering week four of the botched health-care rollout, and with hundreds of millions of taxpayer dollars spent for a system that still does not work, Congress and the American people deserve answers,” the panel’s chairman, Rep. Fred Upton (R-Mich.), said in a statement.

“And as the administration continues to withhold important details and enrollment figures, I hope Secretary Sebelius is ready to give answers and finally live up to the president’s celebrated claims of transparency.”

Plenty of red flags

There were ample warning signs that the system was not working properly, according to people familiar with the project.

The Centers for Medicare and Medicaid Services (CMS), the federal agency in charge of running the health insurance exchange in 36 states, invited about 10 insurers to give advice and help test the Web site.

About a month before the exchange opened, this testing group urged agency officials not to launch it nationwide because it was still riddled with problems, according to an insurance IT executive who was close to the rollout.

“We discussed . . . is there a way to do a pilot — by state, by geographic region?” the executive said.

It was clear at the time, the executive said, that the CMS was still dealing with the way the exchange handled enrollment, federal subsidies and the security of consumers’ personal information, such as income.

One key problem, according to a person close to the project, was that the agency assumed the role of managing the 55 contractors involved and had not ensured that all the pieces were working together.

Some key testing of the system did not take place until the week before launch, according to this person. As late as Sept. 26, there had been no tests to determine whether a consumer could complete the process from beginning to end: create an account, determine eligibility for federal subsidies and sign up for a health insurance plan, according to two sources familiar with the project.

People working on the project knew that Oct. 1 was set in stone as a launch date. “We named it the tyranny of the October 1 date,” said a person close to the project.

“We are working around the clock to identify issues with the site, diagnose them and fix them,” said Joanne Peters, a spokeswoman for Health and Human Services. “We know the site is working significantly better than it was on day one, with more people able to get through the process and enroll everyday, but we still have more work to do. We have to get this right so that everyone who wants coverage can get it, and we are committed to doing so.”

Initial problems centered on account registration, a function that takes place early in the process and was in part a responsibility of contractor QSSI. While that function has improved, it is not fixed, according to the person close to the project.

QSSI said that a critical component that involves identity management is “successfully handling current volumes,” said Matt Stearns, a spokesman for UnitedHealth Group, the parent company. He said the “entire federal marketplace” was overwhelmed by consumer interest at launch.

The administration had asked CGI to come up with a solution to replace the identity-management piece provided by QSSI, according to documents given to a House panel. But work on that solution has stopped, according to a person familiar with the project.

Additional problems are now showing up in the shopping and enrollment parts of the process, applications that are largely the responsibility of CGI, the person said. Those issues would have shown up earlier if testing had been done sooner, the person said.

CGI built the shopping and enrollment applications to accommodate 60,000 users at the same time. U.S. Chief Technology Officer Todd Park has said that the government expected HealthCare.gov to draw 50,000 to 60,000 simultaneous users but that the site was overwhelmed by up to five times as many users in the first week.

In a statement, CGI said its teams, along with the CMS and its other contractors, “are working around the clock toward the improvement of HealthCare.gov, a system that is complex, ambitious and unprecedented. We remain confident in our ability to deliver continuous improvement in system performance and a more positive user experience.”

Delay the mandate?

White House officials said Monday that it was premature to talk about delaying the individual mandate for those who did not obtain insurance because of enrollment problems. Press secretary Jay Carney said the law already provides a way of removing the tax penalty for those who could not sign up for coverage.

“The issue is, do you have access to affordable health insurance? And the individual responsibility provision is there for those individuals who, even though they have access to affordable health insurance, do not purchase it and therefore are held responsible for that,” he said. “The law addresses that as written.”

Juliet Eilperin, Amy Goldstein, Sarah Kliff and Sandhya Somashekhar contributed to this report.