The chairman of the Federal Communications Commission, Julius Genachowski, on Friday announced his resignation in the “coming weeks.”

The country’s top telecommunications regulator told a staff meeting of his decision this morning. Genachowski has hewed a middle line between the desires of public-interest groups and the telecom industry, which hasn’t enamored him to either side.

Genachowski’s focus on expanding access to high-speed wireless Internet service, or mobile broadband, broke with some priorities of his predecessors. His FCC levied no fines for broadcast indecency, after a flurry of penalties under Republican chairmen from 2003 to 2008, and he didn’t complete a loosening of media-ownership rules.

“For those of us who represent the public, Chairman Genachowski’s term can best be described as one of missed opportunities,” said public-interest group Public Knowledge. Genachowski should have done more to assert the FCC’s authority over broadband, which is lightly regulated compared to the telephone, and to prevent consolidation in the industry, it said.

Rob Atkinson, president of the Information Technology and Innovation Foundation, a non-partisan think tank, commended Genachowski’s FCC for its National Broadband Plan — the first comprehensive federal plan to stimulate the buildout and uptake of high-speed Internet access — and for its efforts to bring put more radio spectrum to use wireless broadband.

“America’s broadband economy is thriving, with record-setting private investment, unparalleled innovation in networks, device and apps, and renewed U.S. leadership around the world,” Genachowski said Friday as he thanked the FCC’s staff.

Genachowski’s departure will follow that of Republican Robert McDowell, which leaves the five-member commission with a 2-1 Democratic majority until President Obama appoints a new chairman and commissioner.

To replace the 50-year-old Genachowski, President Barack Obama could elevate either of the agency’s two Democrats, or name a chairman from two new members who will need Senate confirmation. But Stifel Nicolaus analysts Christopher King and David Kaut said they believe the front-running candidate for next chairman is Tom Wheeler, a venture capitalist and former president of two major trade groups, for the cable and wireless industries.

Airwaves Auction

Tasks awaiting the FCC’s new leader include conducting an auction to free airwaves for use by high-speed wireless Internet service, or mobile broadband. The auction that could take place next year would sell access to airwaves voluntarily relinquished by television stations, and pay the broadcasters for giving up their frequencies.

Freeing airwaves is one way to relieve a spectrum shortage that Genachowski made a touchstone of his chairmanship. In a 2009 speech he warned of a “looming spectrum crisis” and he repeatedly drew attention to the need for more airwaves to help handle increasing wireless traffic as Americans move toward mobile computing via smartphones and tablets.

Policy questions include whether to restrict participation in the auction by largest U.S. wireless carrier Verizon Wireless and No. 2 AT&T Inc. to ensure smaller companies capture enough airwaves to remain competitive. The FCC also must decide how many airwaves to reserve for WiFi-like services that can provide access to the Internet without going through a traditional wireless carrier.

Wireless Use

The auction could yield 120 megahertz of airwaves for wireless use, according to the National Broadband Plan Genachowski guided to completion in 2010. That amount is almost one-quarter of the airwaves Obama set as a national goal.

In 2011, Genachowski and the Obama administration opposed AT&T’s bid for No. 4 U.S. mobile carrier T-Mobile USA Inc., saying it would lessen competition, and AT&T under pressure abandoned the $39 billion deal.

Blocking the deal helped spur wireless competition by preserving T-Mobile as a competitor and by protecting the third- largest carrier, Sprint Nextel Corp., from being overwhelmed by a new behemoth, Reed Hundt, a former FCC chairman, said in an interview. Tokyo-based mobile carrier Softbank Corp. is seeking to buy Sprint, which wouldn’t have otherwise happened, Hundt said.

On March 13, Genachowski’s FCC approved T-Mobile’s combination with fifth-largest carrier MetroPCS Communications Inc. Genachowski on March 20 said the agency’s review of Softbank’s $20 billion bid for Sprint was on track for completion by late May.

(The Associated Press and Bloomberg News contributed to this report)