Chip makers are on the verge of breaking down a major barrier to such multimedia advances as realistic video-game animation and high-quality video phones.

The ability to manipulate and transmit complex images and sounds within personal computers and over networks still faces obstacles. But at this week's Microprocessor Forum conference in Burlingame, Calif., four companies will describe a new breed of chips that could eliminate a huge barrier _ processing speed _ and could create a new segment of the industry in the process.

Called media processors, the chips are expected to be six to 50 times faster than Intel Corp.'s fastest general-purpose Pentium in handling specialized multimedia calculations. The designs will also allow multiple functions, such as audio, video and three-dimensional animation, to be crammed on a single chip, suggesting that multimedia PCs and other devices will not only become much more powerful but also much cheaper.

How they will perform these feats is equally important. Semiconductor companies have long sold special-purpose chips that do one multimedia job well, but media processors' key functions are controlled by software. That means that the capabilities of products that use the new chips may be upgraded as the industry changes technologies, without the purchase of new hardware. This is particularly important in multimedia, where many key technical standards are in flux.

Two chip companies that have caught the eye of the industry are Silicon Valley start-ups: MicroUnity Systems Engineering Inc. in Sunnyvale and Chromatic Research Inc. in neighboring Mountain View. While both have yet to produce commercial versions that back their claims, several giant companies are convinced that media processors are one of the next big things in networks and communications. Motorola Inc. and Time Warner Inc., for example, have invested in MicroUnity, as have Microsoft Corp. and Tele-Communications Inc.

Much larger companies are pursuing the same concept. International Business Machines Corp. is expected to introduce an unusual chip design called MFAST at the conference, and TriMedia, a unit of Philips Electronics N.V., will discuss its own media processor.

``We are talking significant horsepower compared to what is on a Pentium,'' says Will Strauss, president of Forward Concepts Co., a market research firm in Tempe, Ariz. Though Intel is likely to use similar techniques on its chips eventually, media processors have a two- to three-year head start, he says. ``It's a tremendous break for these new entrants.''

The companies use an array of new tricks to achieve their staggering speed. Chromatic, IBM and TriMedia use a chip design called very long instruction word, or VLIW, that facilitates performing several operations at once. They are also expected to exploit a new generation of memory chips that have wider paths for sending multimedia information to and from the processor.

MicroUnity uses similar techniques, along with a proprietary production process that allows it to pack three times as many transistors on a chip as the Intel Pentium, which is about the same size. By reducing the distances and associated power requirements, its chips can operate at one billion cycles a second, compared with 133 million for the fastest Pentium now on the market.

John Moussouris, MicroUnity's chief executive officer, says the demand for such capabilities is poised to explode. An all-digital TV, Mr. Moussouris notes, will require simple calculations for each of the million or so dots that make up one frame of video _ and 30 of those frames race by every second.

``The existing media and communications industries have an appetite for computation that's about 100 times greater than the (appetite of the) desktop computer business,'' he says.

Many of the companies' claims remain to be proven. MicroUnity, after working for seven years and raising more than $100 million, doesn't expect to produce working chips until later this year or achieve high production volume before 1997.