POP LIFE; NEW ALBUM SHOWS X HAS GROWN (Published 1982)

''WILD GIFT,'' the second album by X, a Los Angeles rock band, was last year's best rock lp. At least this critic thought so, and so did a number of others, from coast to coast. ''Wild Gift'' combined the pile-driving force of pioneering punk-rock bands such as the Ramones with a more complex lyrical sensibility, ragged-but-right harmony singing that sounded at times like Appalachian mountain music, witty quotes and borrowings from first-generation rock-and-roll stylists like Carl Perkins and Chuck Berry and a wonderfully infectious swing that suggested at least one of X's four musicians - the drummer D.J. Bonebrake, it turns out - had some experience playing jazz.

''Wild Gift'' and X's first album, ''Los Angeles,'' sold more than 100,000 copies on the Slash label. X had approached and been rejected by virtually every major record label before signing with Slash. But when the band's two albums sold spectacularly and received rave reviews, the major labels changed their minds. This year, X left Slash and signed with Elektra, and this week Elektra released the band's first major-label album, ''Under the Big Black Sun.'' X will follow up the release with a July 10 performance at the Palladium.

Nobody, X included, could have topped ''Wild Gift'' for sheer intensity and drive, and the group was wise enough not to try. ''Under the Big Black Sun'' finds X growing, expanding its range, testing its limits. The album includes a bluesy soul ballad, several tunes with a country-and-western flavor, updated Bo Diddley rhythms and X's version of a turn-of-the-century string-band tune originally recorded by Leadbelly for the Library of Congress. Hard-line punk fans will probably accuse X of watering down their music, of selling out. But with ''Under the Big Black Sun,'' X serves notice that they are not about to be confined by any musical orthodoxy, including the orthodoxy of punk. Lyricists Are Idealists

The guitarist Billy Zoom and Mr. Bonebrake have a hand in shaping X's music, but it is the bassist and vocalist John Doe and the vocalist Exene Cervenka who write the lyrics. Mr. Doe and Miss Cervenka are husband and wife, and they are idealists - they believe in what they call ''traditional values,'' which include being faithful to each other.

On ''Wild Gift,'' they wrote and sang about the difficulty of hanging onto their values and hanging on to each other in today's Los Angeles, where sexual experimentation, extramarital affairs and divorce are regarded as not just acceptable but also practically inevitable. They are still grappling with this problem on ''Under the Big Black Sun,'' apparently with mixed success. They're still together, still devoted to each other, but in the song ''Because I Do,'' they ask, ''What kind of fool am I?'' and answer: I am the married kind The kind that said I do Forever searching for someone new. In the album's title tune, they note, ''Adultery makes you give things away/ It gets you confused.''

Shortly before X began recording ''Under the Big Black Sun,'' Miss Cervenka was shattered by the death of her sister Mary in an automobile accident. The most moving songs on the album - ''Riding With Mary'' and the sadly wistful ''Come Back to Me'' -attempt to make some sort of sense out of this senseless tragedy. X is a band that confronts troubling issues head-on and doesn't settle for easy answers.