American Telephone & Telegraph Co. plunged deeper into the turbulent semiconductor market yesterday by announcing that it will begin marketing a state-of-the-art, 32-bit microprocessor computer chip set.

The move puts AT&T squarely in competition with Motorola Inc., Intel Corp., National Semiconductor Corp. and other semiconductor companies that design and manufacture silicon chips. The chips essentially are the computational "brains" of personal computers and other programmable devices such as electronic test equipment.

Ken McKenzie, associate director of semiconductor research for Dataquest, an industry analysis firm based in San Jose, noted that AT&T's microprocessor, which can be found in existing AT&T products, is designed to run the UNIX operating system. The UNIX system, which is the set of internal software instructions that effectively run the computer and its associated hardware, is one that AT&T hopes will become a standard in the computing industry.

AT&T hopes its microprocessor will become the cornerstone of UNIX-based personal computers, scientific equipment and factory automation products.

The market for 32-bit microprocessors -- chips that can process computer "words" that are 32 digits long -- is fairly small right now. The market for 16-bit chips, which most personal computers now use, is approximately $300 million a year.

However, the 32-bit market is expected to grow quickly as users come to demand more and more processing power.

The microprocessor market is just one part of the multibillion-dollar semiconductor industry. In essence, microprocessors are chips that calculate. A major part of the semiconductor market is memory chips, which store computer information.

AT&T also markets a memory chip that can store more than 256 thousand bits of information. It is used in personal computers.