An NTIA spokeswoman didn't immediately respond to a request for comments on the GAO report.

Some Republicans suggested the GAO report brings into question recent and the (PCAST) for government agencies to share some spectrum with commercial users instead of vacating the spectrum.

PCAST based its spectrum-sharing recommendations on an NTIA estimate that it would cost US$18 billion to clear the 1755MHz to 1855MHz spectrum band, Walden said. That spectrum is now used by the U.S. Department of Defense and other agencies, but targeted by the NTIA for commercial use.

There is little spectrum sharing between the government and private entities at the moment, said Mark Goldstein, GAO's director of physical infrastructure issues. "The business model does not work, because of the uncertainty involved," he said.

The private sector may not want to invest in shared spectrum, said Representative John Skimkus, an Illinois Republican. "Having it is better than sharing it," he said. "Give it to the dang private sector and see if they can turn a profit."