WASHINGTON — President Barack Obama on Monday said there was “no excuse” for the cascade of computer problems that have marred the rollout of a key element in his health care law, but declared he was confident the administration would be able to fix the issues.

“There’s no sugarcoating it,” Obama said. “Nobody is more frustrated than I am.”

The president said his administration was doing “everything we can possibly do” to get the federally run websites where people are supposed to apply for insurance up and running. That includes bringing in additional technology experts from inside and outside the government to work on the issues.

People have until March 31 to sign up for coverage. The non-partisan Congressional Budget Office had projected that about 7 million people would gain coverage through the exchanges during the first year.

The president on Monday guaranteed that everyone who wants to get insurance through the new health care exchanges will be able to, even if they have to enroll over the phone or fill out a paper application.

Obama’s event in the White House Rose Garden had the feeling of a health care pep rally, with guests in the Rose Garden applauding as Obama ticked through what the White House sees as benefits of the law. The president was introduced by a woman who had successfully managed to sign up for health insurance through the marketplaces in her home state of Delaware.

The rollout failures have been deeply embarrassing for the White House. The issues have called into question whether the administration is capable of implementing the complex policy and why senior White House officials — including the president — appear to have been unaware of the scope of the problems when the exchange sites opened on Oct. 1.

Obama, in his most extensive remarks about the health care problems, insisted Monday that the health care law is about more than just a website.

“The essence of the law, the health insurance that’s available to people, is working just fine,” he said during his 25-minute remarks.

The White House says more than 19 million people have visited HealthCare.gov since the site went live on Oct. 1. Officials also say a half million people have applied for insurance on the federal- and state-run websites.

Administration officials initially blamed a high volume of interest for the frozen computer screens that many people encountered when they first logged on to the website. Since then, they have also acknowledged issues with software and some elements of the system’s design.

However, the White House has yet to fully detail exactly what went wrong with the online system consumers were supposed to use to sign up for coverage. And Obama on Monday did not explain how the problems in detail or why they were not fixed before sign-ups opened to the public.

Officials say that at this point they are not considering extending the enrollment window beyond March 31. They also say they are not considering taking the website down for an extended period of time to address the problem but instead will do that maintenance during low-traffic overnight hours.

The president did acknowledge that the failures would provide new fodder for opponents of the law, often referred to as “Obamacare.” With the website not working as intended, “that makes a lot of supporters nervous,” he said.

But he said, “it’s time for folks to stop rooting for its failure.”

In an ironic twist, the troubles with the health care rollout were overshadowed at first by Republican efforts to delay or defund the law in exchange for reopening the government during the 16-day shutdown. The bill that eventually reopened the government included no substantive changes to the health care law.

With the shutdown over, GOP lawmakers have been ramping up their criticism of the health care law’s troubles.

“An overhauled website isn’t going to fix the underlying fact that Obamacare is not a workable law,” Sen. Mike Johanns, R-Neb., said. “I urge the president and my colleagues across the aisle to recognize the harm being done and set aside their pride to stop the most damaging provisions of the law, or better yet, to repeal and replace it.”

Associated Press writer Laurie Kellman contributed to this report.

Affordable Care Act 101

• Affordable Care Act 101: We break down the ACA, what it does and what it requires you to do.
• Just the FAQs ma’am: Frequently asked questions and helpful answers
• An ACA Timeline: How health care coverage has evolved.
• Where to get assistance and more info: There are more sources of information and help understanding how the Affordable Care Act affects you.

• Groups tell state panel that interest remains high for ACA