Sony Corp. said it has developed a new miniature audio disc that allows high-quality sound recording and holds as much music as current compact discs.

The new format, called "mini disc," uses discs only 2.5 inches in diameter, about half the size of regular CDs. Each disc is enclosed in a protective cartridge, like a computer diskette.Sony said the system combines the portability and recordability of audio cassettes with sound quality that is nearly as good as CDs.

"It's not quite as good as a compact disc but much, much better than cassettes, in a size that's considerably smaller than a CD," a Sony official said.

Portable stereos using the format will fit inside a shirt pocket, the company said.

Sony plans to begin marketing equipment using the new system in late 1992 and has received a "positive response" from other manufacturers and record companies about adopting the format, the official said.

The miniature discs store sounds in digital form, like CDs, and hold 74 minutes of music by using new digital compression circuitry that eliminates the inaudible portion of sounds but has little effect on sound quality, Sony said.

N.V. Philips, a Dutch electronics maker, has announced a digital tape recorder called the digital compact cassette that also makes use of compression technology. Philips says its sound quality rivals CDs.

Sony and Philips co-developed the compact disc format, which was introduced in 1982.

The optical discs used by CD players cannot be recorded by users. Sony said its new format can play back optical discs made in current CD production facilities but requires different magneto-optical discs for recording.

Sony expects the format will create a new market among people who want portable high-quality sound, the official said.