WASHINGTON — For months, TV viewers have been told by government, by industry and by the media that if they already subscribe to cable, there’s no need to worry about the coming transition to digital broadcasting.

So cable customer Doris Spurk was surprised to learn that thanks to the transition, she would have to rent a converter box for $5.95 per month, per television set, plus pay for a $60 service call to install it. With five televisions in her home, the conversion would increase her bill by 75 percent.

But the 28 million customers who receive analog service — meaning they probably plug their cable wire straight into the back of their set and do not have a set-top box — may have reason to worry. (Satellite customers, except in rare instances, aren’t affected.)