Raleigh, N.C. — An unexpected spike in requests has sapped all the money from the federal program that offers coupons for digital TV converter boxes.

On Sunday, the program received requests for the last of the 51.5 million coupons for which Congress had allotted $1.34 billion. On Monday, it started a waiting list, said Meredith Atwell-Baker, acting assistant secretary of commerce.

Analog TV sets without cable or satellite service need converter boxes to receive a signal after broadcasters begin sending only digital signals on Feb. 17. The coupons subsidize $40 of a converter box's cost, which can go up to $80.

The 7.2 million requests for coupons in December was "a larger number than we had ever predicted. We predicted 4.3 million," Atwell-Baker said.

By Monday afternoon, 103,000 people were on the waiting list, Atwell-Baker said.

Atwell-Baker said the agency expects that about 6 million more coupons will become available as already issued ones expire without being used. The coupons have a redemption rate of about 58 percent in recent weeks.

Those seeking to redeem coupons, though, could face another problem: Retailers could run out of boxes and face a shortfall of 2.5 million boxes, National Telecommunications and Information Administration officials said. Many retailers have stocked boxes based on coupon use.

Those who placed their requests by Sunday will receive their coupons within four weeks. Those on the waiting list were unlikely to receive coupons by the Feb. 17 deadline, Atwell-Baker said.

When consumers call to request coupons, they will be told they are being put on the wait list and given a reference number, which can be tracked online.

Atwell-Baker said that asking Congress for more funding was only one among many options that officials were considering to keep the coupon program going.