WASHINGTON (Reuters) - The Federal Communications Commission on Thursday proposed halving the minimum opening bid on a piece of valuable wireless spectrum, but several commissioners expressed doubt that the plan would work, after an earlier auction failed to attract industry interest.

The five-member FCC approved a draft proposal, subject to public comment, devised by agency Chairman Kevin Martin, cutting to $750 million a prior $1.3 billion minimum bid and easing other requirements.

The aim is to lure commercial interest in the airwaves, which come with a requirement to partner with public safety agencies during emergencies. The airwaves are being vacated as television broadcasters move to digital signals early next year.

The FCC wants to auction them off, and at the same time address a lack of "interoperability" between systems used by first responders that hindered emergency responses during such crises as the September 11 attacks and Hurricane Katrina.

But several commissioners raised doubts that the changes would entice commercial partners to buy the spectrum, for reasons including too-high prices and lack of clarity for public safety officials.

"We are flying blind to some extent," said Jonathan Adelstein, a Democratic commissioner who concurred in part and dissented in part on the changes. "We're expecting major investments are going to be made by private enterprise" without a cost-benefit analysis to make it economically viable.

Of the new $750 million price tag, Adelstein said: "I cannot put my vote behind such a high figure arrived at so arbitrarily."

The other Democratic Commissioner, Michael Copps, said the proposal is unclear as to what public safety officials get for the $48.50 fee they would pay to commercial providers for use of the spectrum.

Republican Commissioner Robert McDowell was also skeptical, but voted to push the proposal through to prevent "analysis paralysis."