WASHINGTON — It's still three years away, but there now is a firm date for the transition to all-digital television — the biggest change in the industry since color TV.

Legislation passed by the Senate yesterday would require broadcasters to end their traditional analog transmissions by Feb. 17, 2009, and send their signals digitally. Such technology promises super-sharp pictures and better sound.

The plan also would allocate as much as $1.5 billion for a "converter box" program to help people with older, analog TV sets that would lose their signal in the digital era. Consumer advocates say that is not enough money.

The digital deadline was part of a larger budget bill that narrowly passed the Senate. House approval is expected and President Bush praised the Senate vote.

Consumers who have newer TV sets capable of receiving digital signals would not notice a change when the switch is made in 2009, nor should satellite television viewers and the roughly 26 million households with digital cable.

Cable industry representatives say there is the potential for a service disruption for some of the 40 million cable customers without digital. If they still have an analog TV set in 2009, they could lose some stations.

For those households, cable operators would convert digital signals back to analog for the major broadcast stations. That may not happen for smaller, independent stations unless those stations and cable operators work out a deal or Congress intervenes.

Analysts expect some agreement.

"It seems likely that Congress will plug this gap at some point before the hard date cutover," said Paul Gallant, media policy analyst at Stanford Washington Research Group.

Under the converter box program, consumers with analog sets would be able to request two $40 coupons to help buy the set-top boxes, which are expected to cost $50 to $60 each.

Democratic lawmakers and consumer groups say that the $1.5 billion would fall far short of helping pay for every set eligible for a converter box.

"We think this is unfair, unworkable and unacceptable. It virtually ensures that on Feb. 18, 2009, tens of millions of televisions go black," said Jeannine Kenney, senior policy analyst with Consumers Union, the publisher of Consumer Reports.

Consumers Union says the fund — after subtracting operating and other costs — would cover fewer than 17 million households.

An estimated 21 million households do not get cable or satellite service and rely solely on free over-the-air TV. Consumers Union estimates an additional 20 million homes that have cable or satellite do not have all of their TV sets hooked up to the service and would need converter boxes.