Since "pop" music is a relatively recent invention (every culture has had its own musical vernacular, but the commercial pop market is barely more than 50 years old), it would not seem a difficult field to research. But, by definition, pop music is transient, intended for impact rather than longevity, a medium as amorphous as the audience it is designed for.

Rock 'n' roll, especially, by its impetuous nature, has resisted the infrequent efforts of statisticians and pigeonholers. With pop music playing an ever-greater role in dictating the rhythm of our society, however, the publishing world finds itself grappling with the task of chronicling the history and progress of this important, if elusive, sphere of human endeavor.

By far the most wide-reaching attempt is the "Contemporary Music Almanac," by Ronald Zalkind (Schirmer Books, $15.95 hardcover, $9.95 paper), the only comprehensive book to put together the human and business aspects of rock 'n' roll, for that is what is meant here by "contemporary music." There are chapters devoted to an informal history of rock; a calender of birth and death dates of rock stars (arranged by astrological signs, no less); Grammy, Academy, Tony, Gold and Platinum award winners; directories of rock books, films and magazines; tips on writing music business contracts, and endless listings of record companies, radio stations, recording studios, concert halls, musicians' unions, producers, publishers, lawyers, publicists, fan clubs and more.

In some areas, such as the chapters on raising money and organizing a business, the mere inclusion of the subject makes this the foremost source, since no one has ever targeted these matters to the record business before.

It is only when the book treads on more familiar ground that its shortcomings are exposed. The longest chapter is devoted to an artists' Who's Who and, although the thumbnail sketches are predominantly accurate, even superstars on the order of The Beatles and Elvis Presley are given woefully short shrift. And instead of discographies with dates and catalog numbers, the least one might expect from an almanac, all that's listed is one or two recommend recordings per artist. There are also some glaring omissions: among the absentees are Harry Nilsson, the Persuasions, Joe South, Al Kooper, Teddy Pendergrass, the Jam, sha Na Na and Johnny Nash, hardly insignificant names in the pop lexicon.

Because of these flaws, the "Contemporary Almanac" fails to eclipse the late Lillian Roxon's "Rock Encyclopedia" (Grosset and Dunlap, $7.95 paperback), an ingenuously charming venture, originally published in 1969 and recently revised by Ed Naha.

Serious rock fans will prefer "The Illustrated Encyclopedia of Rock" (Harmony, $17.95), a more hardcore treatment by Nick Logan and Bob Woffinden, editors of England's New Musical Express. Obscure groups (Can, N.Y. Dolls) and pioneers (Les Paul, Ray Charles) are put in historical perspective, while in-depth consideration is devoted to established stars (the Kinks, Paul Simon). A readable layout, with excellent color and black-and-white graphics, also recommends this book over the competition.

But none of these encyclopedias gives specific release dates or the all-important chart positions from the trade publications. For this data, one must turn to Joel Whitburn's "Record Research," a series of annually updated compilations covering all popular music fields from 1955 to the present (available by mail order only from Record Research Inc., P.O. Box 200, Menomonee Falls, Wis. 53051).

But if the main section of the "Contemporary Almanac" lacks the wit of Roxon, the inside dope of "The Illustrated Encyclopedia of Rock" or the discographies and chronologies of Whitburn's books, the most glaring weakness of the almanac as a lasting document is in the narrowness of its definition of contemporary music. Perhaps Zalkind only intended the book to cover the rock genre (if so, why not call it the "Rock Almanac"?), but the result is that basic styles of American music, such as country & western, gospel, blues, folk, jazz and rhythm & blues, are virtually ignored. Fortunately, several publishers now offer titles that cover at least some of these integral modes of musical expression.

Although "The Illustrated History of Country Music" (Doubleday, $8.95 paperback) is in essay form, limiting its value from a reference standpoint, it manages a definitive breakdown of country music into chronological and geographical sub-genres. Eight authors collaborated on this book but, maddeningly, credit for who wrote what is withheld. One can only acknowledge the editors, Patrick Carr and Country Music Magazine, for tying together in such a vivid manner the vast range of artists, from early hillbilly pickers of the Grand Ole Opry to Dolly Parton.

Another recent arrival, which makes even less of an atempt at objective fact-finding but is worthy of mention, is "Lost Highway" (Godine, $18.95 hardcover, $8.95 paper). It's the second book by Peter Guralnick, a musicologist and critic who writes personalized essays based on meetings with significant country, blues and rock figures such as Charlie Rich, Ernest Tubb and Howlin' Wolf. A more conventional reference book than these two, and equally valuable for that reason, is "The Illustrated Encyclopedia of Country Music" (Harmony, $7.95 paperback) by Fred Dellar, Roy Thompson and Douglas Green. Originating from England, whence one might not expect such expertise in country & western lore, this is part of the same series as the aforementioned "Illustrated Encyclopedia of Rock," and offers the same knowledgeabillity and fine layout. (The series will be extended to include entries on rhythm & blues and classical music in the near future.)

Folk music, perhaps because its practitioners tend to be more literate to begin with, has traditionally fared well in print in the years since the protest song first reared its righteous head. "Baby Let Me Follow You Down" (anchor, $8.95 paperback), by Eric van Schmidt and Jim Rooney, continues this pattern. Written by a couple of insiders (the book takes its name from the title of a song written by von Schmidt and made popular by BOB dylan in 1962), the text tends to be subjectively insulated at times, but that is well within keeping with the era it describes. Again, not a facts-at-your-fingertips source, but a firsthand portrait of a time when popular music, spearheaded by such voices as Woody Guthrie, Pete Seeger and Joan Baez, had its greatest sociopolitical impact.

The blues idiom has also inspired some credible literature, although the bulk of it is long on emotion and characterization and short on linear data. Compensating for this general lack of concrete information is the "Blues Who's Who" (Arlington House, $35), Sheldon Harris' biographical dictionary of blues artists. A voluminous effort (775 pages), it boasts rare photos, birth and death dates, direct quotes, listings of stylistic influences and further sources of information regarding artists ranging from virtual obscurity (clarence "Big" Miller, Bertha "Chippie" Hill) to household names (B. B. King, Muddy Waters). Also featured are extensive song, name and places indices.

The music sections of our bookstores may be dominated by sensational, as-told-to pulp, but that is perhaps to be expected in such an ephemeral and glamorous field. For those whose interest goes beyond what is currently topping the hit parade, however, it is comforting to know that trends andannals are being conscientiously compiled. Although there may never be a single, all-encompassing volume, the "Contemporary Music Almanac" and the other books mentioned here represent a valiant attempt at filling the void. They give us valuable insight into one of the most telling cornerstones of our culture.