U.S. Senate Republicans blocked a bill on Friday that would have delayed next month's nationwide shutdown of analogue TV signals until June 12, but Democrats vowed to bring the measure back for a vote next week.

The bill was defeated even after president-elect Barack Obama on Friday urged lawmakers to postpone the Feb. 17 transition amid mounting concerns that too many Americans who rely on analog TV sets to pick up broadcast channels won't be ready. Obama called for a delay largely because the federal program that subsidizes converter boxes for those viewers hit a $1.34 billion funding limit this month.

But some Senate Republicans fear a delay would confuse people and burden public safety agencies waiting for wireless spectrum that will be freed up by the switch. The opponents also said a delay would be costly for television broadcasters that have spent several years preparing for the analogue shutoff.

Some Republicans also said they do not want to push back the transition date until Congress comes up with a plan to fix the coupon program. It was not immediately clear which Republicans blocked the bill on Friday.

The coupon program allows consumers to request as many as two $40 US vouchers per household to help pay for converter boxes. The boxes, which generally cost $50 to $70 each and can be purchased without a coupon, translate digital signals back into analogue ones for older TVs.

But the National Telecommunications and Information Administration, the arm of the Commerce Department administering the program, is now sending out new coupons only as older, unredeemed ones reach a 90-day expiration date and free up more money for the program.

The NTIA had more than 2.1 million coupon requests on a waiting list as of Wednesday.

Now many Washington lawmakers and policymakers fear that even if the agency could begin sending out new coupons immediately, many consumers would not receive them in time for the Feb. 17 switchover.

"We risk leaving those who are most reliant on over-the-air broadcast television for their information literally in the dark," said Senate commerce committee chairman John D. Rockefeller, author of the Senate bill calling for the delay to June 12.

Despite Tuesday's setback, Democrats plan to bring Rockefeller's bill for a vote again next week.

Switch could affect 10 million households: consumer advocate

Gene Kimmelman, vice-president for federal policy at Consumers Union, fears that as many as 10 million households that depend on over-the-air television may not be taken care of unless Congress finds another $500 million to $1 billion US for the converter box program.

He argues that the government has an obligation to approve the money since it has raised roughly $19 billion US by auctioning off spectrum due to be freed by the analog TV shutdown.

A separate measure on digital TV is scheduled to come up Wednesday in the House. House commerce committee chairman Henry Waxman, a Democrat, also supports delaying the digital transition to June 12 and has proposed reforms to make the coupon program easier for people to deal with.

The digital TV change has already begun in Hawaii, and unprepared residents lit up special help-centre phone lines set up by the Federal Communication Commission and broadcasters. Hawaii went to all-digital TV signals on Thursday so that broadcasters and park rangers could take down analogue transmission towers on the slopes of Maui's Haleakala volcano before the nesting season of an endangered bird.

The Canadian Radio-television and Telecommunications Commission has said that Canada's switch to digital from analogue will take effect by Aug. 31, 2011.