MILLIONS OF PEOPLE encounter the graphic art of Susan Kare every day. Many more will experience her unusual work in the months ahead. Kare's carefully crafted images have won a place among the cultural symbols of our age. Yet few people have any idea who she is or where her work can be seen. Only a handful of industry insiders know that Kare is the artist responsible for the graphic appearance of some of the country's best-known computer software.

Kare, who is based in San Francisco, designed most of the distinctive icons, typefaces and other graphic elements that gave the original Macintosh computer its characteristic -- and widely emulated -- appearance.

Since then, Kare has parlayed her initial work for Apple Computer Inc. into a full-time business, designing graphic user interfaces, or GUIs, for computer companies and software developers. The user interface is the software that allows an operator to control a personal computer and direct its functions. A decade ago, most interfaces forced the user to type cryptic commands in a blank space on the monitor.

With the introduction of the Macintosh in 1984, Apple pushed the world toward the graphic interface, which provides greater ease of use. A graphic interface allows an operator to control the computer by manipulating symbols displayed on its monitor, usually with a mouse or trackball.

Kare's contribution to the growing acceptance of the graphic interface has been to enhance the appearance of the display. Her unusual profession might be described as computer iconographer. ''It's a real niche," she said. "I don't think it's something you'll find in the Yellow Pages."

The personal computer industry moved further toward adoption of graphic interfaces last week when Microsoft Corp. unveiled the long-awaited Version 3.0 of its Windows program. The greatly improved Microsoft product brings many features previously available on the Macintosh to the larger world of personal computers made by International Business Machines Corp. and their counterparts. To improve the visual design of the previous version of Windows, Microsoft turned to Kare.

She declined last week to discuss the scope of her work for Windows, citing Microsoft policy on non-disclosure. Others who were involved in overhauling Windows said, however, that Kare provided a thorough face lift for the program and designed many of the individual graphic features included in Version 3.0. Kare, 36, came to interface design from a traditional academic background in fine arts. Her initial involvement with computer graphics arose when a former high school classmate, Andy Hertzfeld, invited her to apply for a part-time job at Apple. Hertzfeld was the programming wizard who, as a member of the original Macintosh development team, wrote most of the fundamental software for the new computer.

Unlike earlier computers, the Macintosh featured a "bit- mapped" display in which each point of light, or pixel, on the screen was individually controlled by a single "bit" of computer data. Creating icons and other graphic images was a matter of deciding which bits to turn on and turn off.

Macintosh icons consist of a grid 30 pixels by 30 pixels -- 900 dots in all. "I pay attention to every dot," Kare said. "If you like needlepoint, you'll love bit-editing." Kare works almost entirely on a computer, shunning traditional artist's tools for their electronic successors. "Anything that's bound for the screen, I do on the screen," she said.

Although computer iconography may be a new specialty, Kare traces its lineage to ancient roots. "There are ways people have expressed themselves in the past that are analogous," she said. The tile mosaics of the Romans can be thought of as an early form of bit-mapped graphics, said Kare, who holds a doctorate in art history. Similar techniques appear in medieval weavings and tapestries.

When Steve Jobs left Apple and formed Next Inc., Kare soon followed as creative director, responsible for establishing graphic standards and a corporate identity for the new firm. To create the Next logo and related graphic materials, the company hired one of her professional idols, the legendary Paul Rand.

Perhaps the country's most influential graphic designer, Rand had created such enduring symbols as the IBM logo and those of Westinghouse Corp., American Broadcasting Co. and United Parcel Service. ''His work is clear and memorable," she said, choosing her terse description as carefully as she crafts an icon.

Two years ago, Kare left Next to establish her own business focused entirely on design of graphic interfaces. The computer industry's steady march toward better graphics has provided her an abundance of work. ''I didn't have to sit around waiting for the phone to ring," Kare said. Many of her assignments have come from the large network of Apple alumni who have moved on to new ventures. "A lot of my friends are ensconced in other companies needing interfaces," she said.

Kare's work falls into two categories. Software companies with existing products often turn to her to improve the appearance of their programs. These clients "want cosmetics," she said. The other type of customer brings Kare into a project at an earlier stage, when particulars of a proposed product are under discussion.

The growing demand for graphic user interfaces has forced Kare to turn down work. She has rejected potential clients in part because she refuses to hire people to share the work load. "I do every job myself because I think of it as an art," she said. If there is a secret to her work, it is simplicity, restraint and common sense. Adding too many details to an icon renders the result less legible on a computer screen. But using too few details obscures the meaning of the icon.

These days, Kare must pay attention to legal considerations as well. Apple is suing Microsoft and Hewlett-Packard Co. for copyright infringement, charging in part that aspects of their graphic interfaces are too similar to features of the Macintosh software.
Kare said that most of what she does is "optimizing for things that look good on the screen." The soundness of Kare's approach is evident in the widespread adoption of her work and the emulation of her graphic techniques in software designed by others. ''It's really gratifying to go to a (computer) show and really see a lot of these applications," she said.