WASHINGTON — The surveillance court that oversees the U.S. government’s massive collection of telephone data gave its fullest defense, to date, this week of why it considers the program lawful, despite the uproar it received after its existence was exposed earlier this year. 

Britain’s Guardian newspaper disclosed the telephone database’s existence in June, which exposed that the U.S. government warehouses daily telephone “metadata,” such as numbers called and the length and time of calls going back seven years. It does not include the content of calls or the names of callers, U.S. officials have since said.

In an opinion dated August 29 and released on Tuesday, Sept. 17, Judge Claire Eagan of the U.S. Foreign Intelligence Surveillance Court wrote that the program did not violate the basic privacy rights of Americans and was authorized under the 2001 law known as the Patriot Act

U.S. officials have said the database is valuable in preventing attacks by al Qaeda and other militant groups, and that access to the database is limited to trained personnel who are investigating international terrorist organizations.

The Foreign Intelligence Surveillance Court reviews the program periodically, but its opinions generally are classified and are rarely known to the public.