Marilyn Tavenner will be the first Obama administration official to appear before Congress on the troubled (Manuel Balce Ceneta/AP)

Marilyn Tavenner is head of a $1 trillion-a-year agency that provides Medicare and Medicaid coverage to 90 million Americans — and is overseeing the implementation of President Obama’s health-care law.

As recently as late September, she predicted that the Affordable Care Act would have a smooth launch on Oct. 1.

“I talked to Marilyn a lot before the rollout, and I think she was surprised by how it’s gone,” said Thomas Scully, a Medicare administrator under President George W. Bush and a longtime colleague of Tavenner’s. “She seemed pretty confident it would work.”

On Tuesday, Tavenner will be the first Obama administration official to testify before Congress about the efforts of her agency — the Centers for Medicare and Medcaid Services — to implement the 2010 law. The agency recently hired contractor Quality Software Services Inc. to be the general manager for the effort to fix the troubled Web site.

Tavenner is likely to face a barrage of questions about the lead-up to the site’s botched debut — as well as the administration’s previous claims that everything was on track for a successful launch.

A look at the consumer's route through the website and the potential failure points.

“We will focus on oversight of why the testing did not occur; why the administration told this committee repeatedly that they were on track when they were not; the uncertainty this is causing for Americans trying to sign up, wondering if their doctor will still take their coverage, seeing cancellations of their current health-care plan,” said a spokeswoman for the House Ways and Means Committee, which will hold the hearing.

On Monday, White House press secretary Jay Carney acknowledged that some consumers would lose their “substandard plans” and have to pay higher premiums because of the new law.

“It’s true that there are existing health-care plans on the individual market that don’t meet those minimum standards and therefore do not qualify for the Affordable Care Act,” he said.

The administration, meanwhile, tried to focus the debate on affordability, issuing a report that said that nearly half of uninsured young adults —46 percent of those ages 18 to 34 — should be able to purchase a plan through the Web site,, for a monthly premium of $50 or less.

As Medicare’s first confirmed head in nearly a decade, Tavenner has had unusually strong bipartisan support, including the endorsement of House Majority Leader Eric Cantor (R-Va.).

Cantor and Tavenner got to know each other when they worked in Richmond — she as a hospital executive and he as a politician. Along with many of his colleagues, Cantor has focused on Health and Human Services Secretary Kathleen Sebelius as the main person to blame for the troubled health-care rollout.

“The problems with Obamacare transcend the Web site or one office within HHS,” Cantor spokeswoman Megan Whittemore said. “Tavenner’s recent appointment was encouraging, but this law is unfixable. More concerning is Secretary Sebelius’s mismanagement since Obamacare became law.”

Tavenner joined the Obama administration in April 2010 after a decades-long career in Virginia hospitals. She began her career as an intensive-care unit nurse in Richmond.

She eventually became a chief nursing officer and then the chief executive of two Virginia hospitals owned by the Hospital Corporation of America, one of the country’s largest hospital chains. In 2004, she became HCA’s president of outpatient services.

Tavenner left the corporate world the following year, when then-Virginia Gov. Timothy M. Kaine (D) appointed her to serve as the state’s secretary of health and human resources.

“Marilyn’s background as a leader in hospital administration and Medicaid has been a real asset,” said Mark McClellan, who ran Medicare under President George W. Bush.

The Senate confirmed Tavenner, who at the time was acting CMS administrator, as administrator by 91 to 7 in May, making her the first confirmed Medicare chief in seven years.

“There’s generally a positive feeling about her, and I certainly share that,” said Bruce Vladeck, who headed Medicare in the Clinton administration and is now a senior adviser at health-care consulting firm Nexera. “She’s very accessible, very direct and very open. She’s clear-sighted about aims and priorities.”

Tavenner’s agency continued issuing guidance on the new law Monday, explaining a decision last week that gives consumers more time to buy insurance before facing the individual mandate’s fines.

Individuals who purchase coverage through the marketplace late in the open enrollment period will “be able to claim a hardship exemption” from the mandate when they file taxes with the Internal Revenue Service in 2015.

Juliet Eilperin contributed to this report.