Two U.S. newspapers are reporting that the National Security Agency collects less than 30 percent of calling data from Americans. That's despite the agency's massive daily efforts to sweep up U.S. phone records.

The reports cite anonymous government sources. The Washington Post and The Wall Street Journal report the NSA's phone data collection has dropped off since 2006. They cited an inability to keep pace with a surge in cell phone usage and dwindling land line use by American consumers.

The Post says the NSA takes in less than 30 percent of all call data; the Journal says it is about or less than 20 percent.

Government officials have said the bulk data collection needs to be massive to search for terror threats. National security officials did not immediately comment.