A much-anticipated legal opinion from the U.S. Government Accountability Office regarding the FCC’s controversial 800 MHz rebanding order should be released next month, a GAO official said today.

“We’ve begun writing it, and we expect it to be out in October,” said Susan Poling, the GAO’s managing associate general counsel.

Sen. Frank Lautenberg (D-N.J.) requested the legal opinion, which is expected to clarify whether the FCC overstepped its authority in the order, which is designed to alleviate interference to public-safety communications in the 800 MHz band caused primarily by Nextel’s operations.

In the order approved unanimously by the commission in July, Nextel would pay at least $3.2 billion to reband all users in the 800 MHz band and contribute 8.5 MHz of spectrum—valued at $1.6 billion—to public safety in the 700 MHz and 800 MHz bands.

FCC officials have said the agency is within its right to make such an order, which they contend is a spectrum swap. However, critics argue that the order effectively is a spectrum sale, the proceeds of which are only supposed to be disbursed by Congress.

Contrary to several published reports, the GAO is not conducting an official investigation into the matter but has been researching the situation in order to issue a legal opinion, Poling said.

Many analysts and industry observers believe the GAO opinion represents the greatest threat to the 800 MHz order, which was before the FCC for more than two years. Although approved in July and released in August, the 256-page order has not been sent to the Federal Register for publication, after which Nextel has 30 days to decide whether to accept the responsibilities associated with the rebanding order.