WASHINGTON (AP) — A top Obama administration official is apologizing for the problems that have kept Americans from successfully signing up for coverage at the government's health care website.

Marilyn Tavenner, the head of the Medicare program, told a House panel that "the website has not worked as well as it should."

Tavenner is the first senior official to publicly answer questions from lawmakers. She's being grilled not only on what went wrong with HealthCare.gov, but also whether lawmakers can rely on promises to have things running efficiently by the end of November.

The Medicare chief told lawmakers that improvements are happening daily. She wouldn't provide current enrollment numbers, saying repeatedly that they won't be available until mid-November.

Her appearance followed last week's testimony from outside contractors who said there hadn't been enough time to test the complex online enrollment system. It froze up on the day it was launched, October first.

The Republican who heads the House Ways and Means Committee, Dave Camp of Michigan, is asking whether it's fair for the IRS to impose penalties on those who don't sign up for health care, if people "can't navigate" what he calls a "dysfunctional and overly complex system."