WASHINGTON — House Republicans warned the Federal Communications Commission on Wednesday against “giving away” scarce airwaves that they said could produce up to $19 billion in proceeds if they were instead auctioned to telecommunications companies for use in mobile broadband networks.

The remarks, which came at a House communications subcommittee hearing, took aim at one of the top priorities of Julius Genachowski, the F.C.C. chairman: to make available more unlicensed airwaves, or spectrum, to open congested mobile broadband networks and to use in Wi-Fi hot spots.

In September, the F.C.C. proposed freeing 12 to 20 megahertz of spectrum for those unlicensed uses. The unlicensed space on the electromagnetic spectrum would also be used as “guard bands.” Those are areas that border segments of airwaves that are used by cellphone companies, broadcasters and other communications entities; their purpose is to limit interference from transmissions on nearby airwaves.

Mr. Genachowski defended the commission’s plans. “Unlicensed spectrum has a powerful record of driving innovation, investment and economic growth — hundreds of billions of dollars of value creation for our economy and consumers,” he told the committee on Wednesday.