In several tweets, Buckman responded: "Going below 24 won't happen ... there's only a small risk we will not continue to exceed our performance standard ... Since 1995, GPS has never failed to exceed performance standards."

To minimize potential disruptions, the GAO recommended that the defense secretary appoint a single authority to oversee development of GPS, including space, ground control and user equipment, to ensure that all the parts are synchronized and that potential disruptions are lessened.

Officials at the oversight committee and the GAO said it is too early for a committee response.

Wireless carriers that provide GPS to customers are aware of the state of the GPS system and recent concerns raised by the GAO, said John Walls, vice president of public affairs for CTIA in Washington, an industry group representing many carriers.

Walls noted that there is less than a 5% chance of a satellite problem, but should one occur, the accuracy of the location of a person using 911 from a wireless phone might be reduced, or it might take longer to identify a customer's location. Still, Walls noted that several satellites could be out of service "without causing significant problems for most wireless applications."