The country’s top communications regulator on Thursday rejected calls to dedicate more airwaves for smaller wireless carriers in an auction expected next year.

Tom Wheeler, the chairman of the Federal Communications Commission, wrote in a blog post that he wanted to keep the level sold exclusively to smaller carriers at the level agreed to last year. T-Mobile US and other smaller wireless carriers lobbied for months to increase the size.

As Americans spend more time using their cellphones, the F.C.C. wants to dedicate a larger portion of available spectrum to cell service. Spectrum is the airwaves through which television, radio and many other signals are sent.

To do so, the agency is buying back rights sold to local TV stations decades ago. It then plans to sell them back to cell carriers, helping them improve service nationwide.