In 1986, a relatively obscure publisher on the West Coast put out a fat volume entitled The New Papyrus, which predicted the death of the reference book. The theory was that atlases, encyclopedias, almanacs etc. would move away from the traditional paper-and-ink format to a new and better universal medium, the CD-ROM.

At first, this seemed just one more droplet in the vast sea of dubious futurology. But The New Papyrus was different, because its publisher, Microsoft -- actually, Microsoft Press, the book arm of Bill Gates's software empire -- was in a position to make the prediction come true. Even as Papyrus was published, Microsoft was at work on the CD-ROM that was to revolutionize the reference industry: the Encarta Encyclopedia.

Until five years ago, the very word "encyclopedia" evoked an unwieldy collection of weighty tomes that stretched across three feet of bookshelf and cost $1,200 or so. The comedian Phil Silvers had a hilarious routine about a nerdy librarian who insisted on taking his entire Britannica along on a vacation. Ridiculous!

Microsoft's Encarta changed all that. It was a single two-ounce disk that fit in a coat pocket and cost $29.95 -- although many computer dealers threw it in for free to spur PC sales. It went anywhere a laptop computer went. It had all the information found in a 20-volume encyclopedia. It also had material that no book had ever provided. A traditional encyclopedia could tell you, for example, that men from Earth landed on the moon on July 20, 1969. A CD-ROM edition provided the same information -- but with the multimedia encyclopedia, you could also watch that first booted foot stepping onto the dusty lunar surface and hear the human voice that crackled through the cosmos: "Tranquility Base, the Eagle has landed." A printed encyclopedia could tell you that Stravinsky's "Rite of Spring" caused a riot in the audience when it premiered in 1913. A CD-ROM edition provided the same information -- but also let you hear the shocking music and follow the score, with each measure highlighted as it played.

Microsoft's "new papyrus" proved such an improvement on its bulky old multi-volume competitors that Encarta was a massive publishing success. By 1995 it was the world's best-selling encyclopedia, and remains so. Traditional publishers -- Grolier, Compton's, and even the legendary Britannica -- resisted briefly but all have now moved to CD-ROM editions, in each case a much cheaper product than the book version.

Of course, you have to buy a computer to use the thing. But even with the price of a home computer thrown in, a CD-ROM encyclopedia costs less than the old printed versions. Eons ago, when I bought The World Book for our first child, I incurred two years of monthly payments. The other day I bought our youngest the same encyclopedia -- for the price of a carry-out pizza.

To substitute a single inexpensive multimedia disk for a costly 32-volume encyclopedia seems an obvious choice. But does it also make sense to replace a concise, easy-to-use reference book -- say, a dictionary -- with a CD-ROM edition that is priced roughly the same? This fall, St. Martin's Press and Microsoft have given us an excellent way to test that proposition. Their brand-new Encarta World English Dictionary (St. Martin's & Microsoft; 2,078 pp., $50)is the most ambitious dictionary of our language since the estimable Random House Unabridged came out 30 years ago. And this new dictionary is available in two forms. St. Martin's has published the work as a book, and it is a splendid example of bookmaking -- sturdy, attractive, easy to read. Meanwhile, Microsoft has brought out a CD-ROM version that is fast, colorful, and a snap to use (Microsoft single-disk CD-ROM, $39.95).

In either format, this is a marvelous dictionary. The definitions are uniformly user-friendly -- clear, complete and easy to understand. Look, for example, at the word "gas." In the Random House Unabridged, the definition starts like this: "a substance possessing perfect molecular mobility and the property of infinite expansion . . ." Encarta is simpler and better: "a substance such as air that is neither solid nor liquid at ordinary temperatures . . . " Encarta's pronunciation guides, too, are written in a plain phonetic alphabet; the usual fancy symbols have been eliminated (except for the schwa, that backward e that no lexicographer can resist). The etymologies are interesting and chatty. For many words (e.g., "jingoism," "panorama," "posh," "rosary"), the etymology is longer than the definition.

Just off the presses, the dictionary is stunningly up-to-date. "Air play," "digerati," "gonk," "veggie burger" and "wannabe" are all here. "Bad" is defined both in the traditional ("below an acceptable standard") and the Michael Jackson ("extremely good") senses; similarly, the definitions for "wicked" include "very impressive or very skillful." "Spam" is listed both as food and as junk e-mail, with an intriguing etymology that cites Monty Python.

There are mysterious gaps. Perhaps "day trader" came along too late for inclusion, but why would an English dictionary leave out the word "salary"? The teenagers in our house were astonished that neither "stoner" nor "phat" made the book. The traditional meaning of "goofy" ("silly or unintelligent") is listed, but not the skateboard/snowboard sense of the word ("right foot forward"), which is probably the most common use of "goofy" nowadays.

Inevitably, perhaps, with 100,000-plus entries, there are mistakes. A "vegan" is defined as "someone who does not eat meat, dairy products, or eggs." Actually -- as the CD-ROM version of the same dictionary makes clear -- a vegan avoids all animal products, including fish, gelatin, etc. This is the only dictionary I've ever seen that says "gambol" is pronounced "gamble." "Gambol" rhymes with "jam bowl," doesn't it?

But these minor logomachies (to use a great dictionary word) are like hemidemisemiquavers (to use another) in a mighty symphony. All in all, the new Encarta is a terrific new reference source. It's the place I'll turn the next time I flip open a dictionary to look up a word.

But will I open a book for that purpose? Maybe not, because I like the CD-ROM version of Encarta's dictionary even better than the book. The disk includes the entire dictionary (with pictures in color, unlike those in the book). But it also holds a thesaurus, a book of quotations, a world almanac and a guide to grammar and style. You type in a word -- the program is tolerant of bad spelling -- and Encarta finds it in any or all of those sources.

The biggest advantage of the CD-ROM, though, is multimedia, which enhances a dictionary just as it does an encyclopedia. The printed dictionary defines a "didgeridoo" ("Australian Aboriginal musical instru-

ment . . . "); the disk edition lets you hear one as well. The printed definition of "counterpoint" is fine as far as it goes ("the sounding together of two or more musical lines . . . "). But the CD-ROM includes a Palestrina excerpt so you can hear, and understand, how four musical lines blend into a contrapuntal texture.

Which, then, is better?

The printed dictionary offers a pleasantly familiar tactile sense that no keyboard can match. Browsing, too, is better in a book -- and this new dictionary, with its clear layout and many pictures, is a joy to browse around in. As for speed: If you suddenly have to look up one word, opening a book is faster than launching a software program. But if you keep the Encarta dictionary software open on your PC (no problem if you have enough RAM memory), the CD turns out to be faster for regular use. And it has so much more information.

The CD-ROM is also faster than any of the many dictionaries now available for free on the Internet. Some day, when we all have high-bandwidth instant connections to the Web, an online dictionary might be useful. Today, it's so slow that the whole idea is a nonstarter ("something or somebody unlikely to succeed").

So I'm delighted with my sturdy new reference book, the Encarta World English Dictionary. This comprehensive, carefully planned volume has earned a place on the dictionary stand beside my desk. But it may spend its days there gathering dust, because I've found that I use the e-dictionary much more often than its paper-and-ink cousin.

T.R. Reid, The Washington Post's London bureau chief, is a veteran reviewer of dictionaries and the author of "Confucius Lives Next Door."