The stodgy old TV set is on the brink of one of the biggest shifts in technological design in three decades. On the surface, the switch to digital TV will not alter the boxy profile or immediately change the quality of the image blinked on the screen. But over the next decade, fundamental changes inside the home television receiver are expected to add new capabilities - such as allowing viewers to watch two programs at once - and deliver better sounds and pictures than today's sets. Eventually, the line between the TV and computer will become blurred.
''Digital TV will not come suddenly and impressively like color,'' says David Fischer, an analyst with Arthur D. Little Inc. ''But its impact is probably going to be just as great in the long run.''
To do all this involves replacing much of the innards of today's TV receivers - several hundred transistors, capacitors, and coils - with a handful of powerful semiconductor chips. Digital electronics, the building blocks of computers, are already used in some sets - in electronic tuning, for instance. The new TV generation will be almost all digital.
This shift is part of a broad move toward using digital codes in many fields, from telephone systems to phonographs. Leading the digital TV derby is International Telephone & Telegraph (ITT), which has developed a set of integrated circuits for TVs.
Most of the world's major TV-makers are also working on digital, but sets won't show up on store shelves until next year. At first many makers, such as Zenith and General Electric, are expected to use ITT chips in their sets to avoid the money-draining chore of developing integrated circuits of their own.
The first digital sets won't transform TV viewing. Other than perhaps subtle changes in clarity and sharpness, pictures will look much the same. But digital is better at eliminating irksome interference and double-image ''ghosts,'' as well as fine-tuning color hues.
Because there are fewer parts, sets are also less likely to break down and easier (though not necessarily cheaper) to repair: Computers can be used to adjust pictures, or engineers can simply replace a chip. A big plus for the makers will be the ease with which features can be added to upgrade sets. No need to develop all-new circuitry. Just reprogram the digital electronics.
''I don't see a dramatic change in the picture in the first sets,'' says William Hittinger, executive vice-president of the RCA Corporation's David Sarnoff Research Center. ''We will be hard pressed to emulate the analog sets at first.''
In digital sets, conventional sound and picture signals are converted into the ''ones'' and ''zeros'' of computerspeak, processed, then converted back to analog wave forms before being beamed to the picture tube for viewing. Converting the signal to digital allows more precise processing, which should sharpen the image.
The real power of digital, though, will come later, in ''add on'' features and in second-generation sets. Advanced chips will allow viewers themselves to freeze frames (for instance, stopping a pitch by Fernando Valenzuela) or zoom in for a close-up (Valenzuela grimace when his pitch goes over the right-field fence).
There is also the potential of carrying two or more programs at once, one of them in a postage-stamp corner of the screen. It will be possible to hear shows in two languages. Promising, too, is the capability to create higher-resolution pictures. In effect, the computer on a chip can double the number of lines ''painted'' on the screen to make the picture sharper, or increase the number of picture frames shown each second to end flicker.
Eventually, digital electronics may add enough flexibility to the TV to make it the hub of tomorrow's home communications center. The sets will be better equipped than current models to carry Information Age functions such as videotex and video games.
People may not beat a path to their local TV store. The first sets will be expensive. ITT's ''Digivision,'' for instance, will sell for roughly $900 in Europe this fall, according to Robert Allen, an ITT vice-president. But as the price of chips dips, the sets are expected to become competitive with more standard models.