WASHINGTON — The Federal Communications Commission voted yesterday to open up unused, unlicensed portions of the television airwaves known as "white spaces" to deliver wireless broadband service.

The vote is a big victory for public interest groups and technology companies such as Google Inc. and Microsoft Corp. that say white spaces could be used to bring broadband to rural America and other underserved parts of the country.

"White spaces are the blank pages on which we which we will write our broadband future," said Jonathan Adelstein, one of two Democrats on the five-member commission. Adelstein added that white spaces could represent a "third channel" to reach consumers beyond the telephone and cable networks that represent the primary competition in today's broadband market.

The vote came over the objections of the nation's big TV broadcasters, which argue that using the fallow spectrum to deliver wireless Internet access could disrupt their over-the-air signals. Manufacturers and users of wireless microphones — including sports leagues, church leaders and performers of all stripes — have also raised concerns about interference.

The next step for opponents could be a fight on Capitol Hill or a lawsuit to stop the FCC plan from taking effect.

"Every American who values interference-free TV should be concerned by today's commission vote," the National Association of Broadcasters said in a statement.

Four commissioners voted to approve the plan with one commissioner — Republican Deborah Tate — dissenting in part. Among her concerns, Tate raised questions about how potential interference problems would be handled.

The FCC plan will allow the use of white spaces to provide broadband following the upcoming transition from analog to digital TV broadcasting in February, which will free up additional wireless spectrum. That space could also be used for improved communications networks to connect police officers, firefighters and other emergency responders.

Supporters say the vacant spaces between TV channels — which would be available for free, unlicensed use, as Wi-Fi is — are particularly well-suited to providing broadband since they can penetrate walls, carry a great deal of data and reach a wide geographic area. FCC Chairman Kevin Martin, one of three Republicans on the commission, called white spaces "a very valuable national asset."

Opening up this spectrum to high-speed wireless connections has been a high priority for Internet companies, which stand to benefit as more Americans get online. Technology and equipment makers, meanwhile, are counting on a multibillion dollar market for advanced wireless devices to transmit and receive signals, including laptops, personal digital assistants and TV set-top boxes.

With partial dissents by the two Democrats on the five-member panel, the FCC also voted Tuesday to approve Verizon Wireless' planned $28 billion purchase of Alltel Corp. in a deal that will create the nation's largest wireless carrier.

Verizon Wireless, a joint venture between Verizon and Vodafone Group PLC, plans to buy Alltel of Little Rock, Ark., for $5.9 billion plus the assumption of $22.2 billion in debt.