WASHINGTON, Dec 2 (Reuters) - New federal numbers put the number of Americans infected with the AIDS virus each year close to 50 percent higher than previous estimates, activist groups and some media reported, but federal officials denied on Sunday that the data was finished yet.

The groups say the new numbers put the number of people newly infected each year with the virus at 55,000 instead of 40,000. The New York Times, Washington Post and Wall Street Journal all say they have sources confirming this estimate.

But the U.S. Centers for Disease Control and Prevention, which tracks the number of infections, said only that new estimates, using new and more accurate methods, were in the works.

"CDC emphasizes that the new estimates are not yet final," the CDC's top AIDS official, Dr. Kevin Fenton, said in a statement.

"In recent years, CDC has worked to develop an innovative system designed to estimate the number of new HIV infections in a given year. As a result of new technology that can distinguish recent from longstanding infections, the new system will provide the clearest picture to date of new HIV infections in the United States," he added.

"The estimates have been submitted for further analysis and rigorous scientific review to ensure the accuracy of the complex new methods and of the estimates themselves."

One group, the AIDS Healthcare Foundation, asked the CDC to release the figures, given all the speculation.

"We hope that this is not yet another instance of the Bush administration's suppression of information that could be damaging to their image, especially in light of the fact that the spike in new infections is, at least in part, likely due to failed policies of the administration, including the promotion of 'abstinence-only' prevention messages and the failure to promote condom use," said Michael Weinstein, president of AIDS Healthcare Foundation.

The CDC estimates that more than 1 million Americans are infected with the human immunodeficiency virus that causes AIDS.

Just last month, the United Nations AIDS agency UNAIDS sharply revised downwards its own estimate of how many people globally have HIV -- from close to 40 million people to 33 million.

UNAIDS said the numbers both reflected good news -- that AIDS prevention measures were working -- and more accurate methods of estimating infection rates. Because it is not possible to count every person infected with the virus, researchers use complex formulas to estimate the numbers.

(Reporting by Maggie Fox)

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