For at least six years, law enforcement officials working on a counternarcotics program have had routine access, using subpoenas, to an enormous AT&T database that contains the records of decades of Americans’ phone calls — parallel to but covering a far longer time than the National Security Agency’s hotly disputed collection of phone call logs.

The Hemisphere Project, a partnership between federal and local drug officials and AT&T that has not previously been reported, involves an extremely close association between the government and the telecommunications giant.

The government pays AT&T to place its employees in drug-fighting units around the country. Those employees sit alongside Drug Enforcement Administration agents and local detectives and supply them with the phone data from as far back as 1987. …

The scale and longevity of the data storage appears to be unmatched by other government programs, including the N.S.A.’s gathering of phone call logs under the Patriot Act. The N.S.A. stores the data for nearly all calls in the United States, including phone numbers and time and duration of calls, for five years.