Zenith, AT&T; Offer Plan for Digital HDTV : Technology: The system, which could become the U.S. standard, should make it easier to link computers with television.

SAN FRANCISCO —  Solidifying their strong position in the race to develop an American high-definition television (HDTV) system, American Telephone & Telegraph and Zenith Electronics on Monday announced a new all-digital version of the HDTV broadcasting scheme that they will present to the Federal Communications Commission next year.

The companies said that digital transmission--which sends information as a series of ones and zeros rather than as a modulated electrical wave--would reduce interference and assure that even television viewers receiving a weak broadcast signal would see an unadulterated HDTV picture.

HDTV will vastly improve the quality of pictures and sound available on television sets, and the new generation of TVs and related equipment is expected to generate billions of dollars in revenue for consumer electronics companies in the next decade.

Japanese companies have a big lead in HDTV technology, but the FCC rejected the Japanese HDTV system as a standard for the United States because it is not compatible with existing television broadcasts. Following a series of tests beginning next year, the FCC will select a U.S. standard for HDTV sometime in 1993. It now appears it will be a digital system.

In addition to the nearly 2-year-old AT&T-Zenith; partnership, competitors in the U.S. HDTV race include General Instruments, the Massachusetts Institute of Technology, the Japan Broadcasting Corp. (which has developed a modified version of the Japanese system), and a consortium that includes Thomson of France, Philips of the Netherlands, the David Sarnoff Research Laboratory and NBC.

Last month, General Instruments surprised the HDTV world with the announcement that it had developed an all-digital HDTV format, and the Thomson-Philips group said it would have a digital system as well.

Dale Cripps, publisher of HDTV Newsletter, said he would not be surprised if MIT came out with a digital proposal, but added that too little technical information was available about any of the systems to judge which was better.

Digital HDTV, in addition to offering better quality, should also make it easier to link computers with television, since computers also use the ones and zeros of digital code as their internal language. The merger of television and computers is seen by many as the next wave in electronics.

The new AT&T-Zenith; system will send regular TV signals on existing channels while sending digital HDTV signals on unused channels that currently serve as buffers between stations. The digital HDTV signals are compressed via sophisticated algorithms and then sent at very low power to eliminate interference.

The new proposal also promises to offer better pictures than other HDTV systems by increasing the number of lines on the screen, and by using so-called progressive scan to refresh the image.