Reversing a proposed decision issued in December, the federal government said Wednesday it would continue to cover the use of an increasingly popular procedure to detect heart disease.

The Centers for Medicare and Medicaid Services said it would continue to cover the scanning procedure, despite its earlier misgivings over whether there was enough evidence to justify paying for the tests under Medicare.

The agency said Wednesday that it would continue to leave payments for the scans up to the local insurance carriers it employs to oversee medical claims. Most local carriers have been covering the test, a form of CT scan that can cost $600 or more.

"We found that the evidence is not black and white either way," said Dr. Barry Straube, chief medical officer for the Centers for Medicare and Medicaid Services. Given the overwhelming criticism of the preliminary decision, the agency decided it did not have enough reason to override local carriers' decisions to cover the tests as medically necessary.

"Before we make a significant change in policy, we need more evidence," said Straube, who indicated the agency would still like studies testing whether the scans are medically effective.

Medicare paid for roughly 70,000 of the heart scans in 2006, according to the agency, at a cost of $40 million to $50 million. For people not yet eligible for Medicare, thousands of other such scans were paid for by commercial insurers or from patients' own pockets, at prices sometimes close to $1,000. As many as 1,500 centers around the country are estimated to be offering the scans, with some centers advertising their services.

The agency's decision to continue paying for scans means their use is likely to continue to climb, according to doctors and insurers. Private insurers often follow Medicare's lead on what medical procedures they will pay for.

The scans are now widely promoted as a noninvasive alternative to tests like angiography, which requires the insertion of a catheter into the blood vessels and can cost thousands of dollars. But conventional angiography is typically done only on patients with cardiac symptoms. There is growing concern that the CT scans are being done increasingly on those who show no signs of heart disease, subjecting them needlessly to radiation risks.