Federal officials have been underestimating the number of new AIDS infections in the United States by 40 percent every year for more than a decade, researchers said Saturday.

Using sophisticated testing to identify new infections, the Centers for Disease Control and Prevention concluded that there are about 56,300 new infections each year - not the 40,000 that has been gospel for so long.

The new numbers do not mean that the epidemic is growing in this country, just that researchers have been able to provide more accurate estimates, said Dr. Kevin Fenton, director of CDC’s National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention.

In fact, he said, the number of new infections has remained relatively constant since the late 1990s.

The agency did not release new numbers for prevalence, relying on existing estimates that about one to 1.1 million Americans are HIV-positive. But epidemiologist and AIDS expert Philip Alcabes of Hunter College of the City University of New York noted that the increased incidence indicates that, “There are roughly 225,000 more people living with HIV in the U.S. than previously suspected.”

More than 15,000 Americans die of AIDS each year.

The apparent leveling of incidence has masked some disturbing trends, Fenton added.

While the incidence has been falling among heterosexuals and injection drug users, it has been rising among gay men and young blacks and Hispanics.

Gay men accounted for 53 percent of all new infections in 2006, the most recent year for which data are available. Infection rates among blacks were seven times as high as among white, while the rate among Hispanics was nearly three times as high.

The new data will be unveiled formally today at the International AIDS Conference in Mexico City and published later this week in the Journal of the American Medical Association.

The new estimates are certain to bring calls for increasing spending to combat the epidemic. Even at the old estimate of 40,000 new infections per year, nongovernment organizations were calling for the U.S. to spend at least another $300 million per year in addition to the existing $700 million.

Since the AIDS epidemic began in 1981, the actual incidence in the United States - and, indeed, in the world - has been a matter of controversy. The problem has been that researchers historically have used “by guess and by golly” techniques to extrapolate overall numbers from limited data.

In the case of the world numbers, better data has led to a recent downward revision, a 40 percent decline to about 2.5 million new infections each year and a total of about 33 million people living with the virus.

In the past, U.S. data came primarily by extrapolating HIV infections from the number of newly diagnosed AIDS cases. But as better treatments have lowered the number of people progressing to full-blown AIDS, those estimates have become more tenuous, experts said.

The new numbers rely on newer test that allows technicians to determine whether an HIV infection occurred in the past five months or is an older, long-term infection, as well as wider testing and reporting.

“These data, which are based on new laboratory technology developed by the CDC, provide the clearest picture to date of the U.S. HIV epidemic, and unfortunately we are far from winning the battle against this preventable disease,” said Dr. Julie Gerberding, director of the CDC.

Using the new estimates for 2006, the team also reanalyzed the historical data. They concluded that the number of new infections peaked at about 150,000 per year in the mid-1980s, then declined to about 50,000 per year in the early 1990s.

By the end of that decade, the numbers had climbed back up to the current level of about 56,000 and have remained roughly constant since, they found.

The most disturbing finding, Fenton said, is that blacks are affected more disproportionately than any other racial and ethnic group in the country. In fact, he said, gay and bisexual black men “are one of the most severely impacted groups in the world.”