The virus that causes AIDS is spreading in New York City at three times the national rate  an incidence of 72 new infections for every 100,000 people, compared with 23 per 100,000 nationally  according to a study released on Wednesday by the city’s Department of Health and Mental Hygiene.

The findings, based on a new formula developed by the federal Centers for Disease Control and Prevention, estimated that 4,762 New Yorkers contracted H.I.V. in 2006, the most precise estimate the city had ever offered.

But the city stressed that because the method of estimating infections was new, it could not be said definitively whether the number of new infections in the city had increased or decreased from previous years.

Blacks, and men who have sex with other men, are the groups at greatest risk of contracting H.I.V., the study found. A summary of the new data:

¶Men accounted for 76 percent of new H.I.V. infections and women for 25 percent. (The figures exceed 100 percent because of rounding.)