Federal regulators moved yesterday to speed the adoption of digital television by ordering manufacturers to install the technology in all mid-size TV sets by next spring.

The Federal Communications Commission voted 4 to 0 to shorten a previous deadline by four months, requiring sets ranging in size from 25 inches to 36 inches to be capable of receiving digital broadcasts by March 1. Analog TV broadcasts are to stop by the end of 2006, as long as 85 percent of households have the capacity to receive digital transmissions.

The commission also denied a request from the Consumer Electronics Association and another industry group to eliminate a July 1 deadline requiring half of new mid-size TVs to have digital tuners.

Digital TV can be transmitted over the airwaves, but it uses a different part of the spectrum than analog signals. It is also an ideal way to transmit high-definition television.

Switching to digital transmission will free up the analog bandwidth for other uses, such as wireless voice and data services.

"The objective now is to take steps to bring the transition to a rapid conclusion," said Alan Stillwell, associate chief of the Office of Engineering and Technology at the FCC. Stillwell said manufacturers had been lagging in production of digital TVs.

Broadcasters already offer digital programming and are expected to ramp up their digital offerings over the next few years, with legislators pushing for adoption of the technology.

Gary Shapiro, president and chief executive of the Consumer Electronics Association, said his group was disappointed that the FCC refused to eliminate next month's deadline. Many consumers prefer buying cheaper analog sets, he said, adding that digital TV units cost an average of $200 to $300 more than traditional sets.

"You're not going to tell consumers what they're going to buy," Shapiro said. "It's impossible to mandate."

Further, Shapiro said he was concerned with an FCC proposal yesterday to require all TV receivers larger than 13 inches to have digital tuners by Dec. 31, 2006, six months earlier than the previous deadline.

"You're talking about doubling the price of a [13-inch] TV set," he said.

Broadcasters and wireless industry representatives lauded the FCC's decision as a welcome step. Wireless providers will likely purchase the analog airwaves now being used by television broadcasters.