WASHINGTON - A federal appeals court on Friday said regulators were reasonable in sticking to a June deadline that requires Sprint Nextel Corp. to vacate some wireless channels that will be used by public safety agencies.

The Federal Communications Commission is requiring Sprint, the nation’s third-largest wireless carrier, to clear certain channels by June 26, a move designed to eliminate radio interference with thousands of public safety agencies across the country. The company would essentially swap spectrum with the public safety agencies.

The deadline was set three years ago in an initial order. But last September the FCC, unhappy with the slow progress, told Sprint it must clear out regardless of whether public safety agencies are ready to move out of their spectrum.

Sprint, which said the FCC’s new position was unreasonable, claimed if regulators enforce the deadline it would cripple the network. The FCC has not established any fines and telecommunications analysts said they expect the deadline would be extended.

Sprint, which has spent more than $1 billion in its spectrum relocation efforts so far, said the initial 2005 order considered a simultaneous swap with public safety agencies. But the FCC argued in September that the deadline applies to Sprint regardless of whether public safety agencies are ready to swap.

Reston, Va.-based Sprint, which has operational headquarters in Overland Park, Kan., appealed to the U.S. Court of Appeals for the D.C. Circuit, which ruled that the FCC’s June 26 deadline was reasonable.

“That deadline — which was never premised on a synchronized spectrum swap — has not changed,” according to the court’s ruling. “What has changed are the implications of the deadline: it now appears Nextel might have insufficient spectrum come June because numerous … (public safety) licensees won’t be ready to relocate.”

The court said if Sprint vacates those channels then it’s likely it will immediately reduce radio interference that public safety agencies have experienced.

Jessica Zufolo, an telecom analyst with Medley Global Advisors, said in a note that the court’s decision is a “significant defeat” for Sprint, but expects the FCC will extend the deadline by at least another six months.

Shares of Sprint dipped 15 cents to $7.87 in afternoon trading.