Teen idols separated by a generation, Paul McCartney and Frank Sinatra have each made significant contributions to popular music. Sinatra elevated the art of vocal phrasing to a progressive openness unmatched before the '50s; McCartney, through his work with John Lennon and the Beatles, changed the entire face of rock 'n' roll in the '60s.

So it is doubly sad now that McCartney has put out an album where a single would suffice and that Sinatra has produced an elaborate three-volume set that contains a single album's worth of respectable material.

"McCartney II" (Columbia FC-36511) follows "McCartney" by a decade.

Both are solo, multi-tracked efforts, but they are worlds apart in methodology. The first set was recorded on a Studer four-track with a single microphone. Its makeshift quality served as a final notice that McCartney has broken with the Beatles and their ultra-sophisticated studio technique. There was only one memorable effort on that album, "Maybe I'm Amazed."

There's nothing memorable on the sequel. "II" was recorded on a specially adapted six-track unit that McCartney could plug into directly without having to work with a huge studio console. The unit, transported back and forth from the Sussex farm to the Scotland estate, provided the usual bag of tricks: digital display, vari-speed, echo displacement. Additionally, with the exception of "Waterfalls," all the songs were composed during the actual recording process, tracks being wiped out or mixed in reckless abandon. It woulds like it, too: At $8.98 list, it's a medium-quality demo tape with an irritably lifeless, overly precise and squeaky-clean sound.

The first two cuts, "Coming Up" and "Temporary Secretary" sound like early Devo, with rhythmic artificialty and remote vocals. "Frozen Jap" (recorded before McCartney's Tokyo bust) is one of two instrumentals, complete with a cliched Oriental theme. "Summer's Day Song" is a simple ballad (one verse only) with classical overtones deserving future development. "Bogey Music" is a sedate rockabilly cop, "Darkroom" is pseudo-disco and "On the Way" is a weak blues stroll. McCartney's no longer charting new pop trends, but at least he's still listening to them.

The two respectable songs on the album are "Front Parlour" and "Waterfalls." The first is an instrumental track with a catchy, clever melody in the manner of Beaver and Krause. Even this one soundslike it's waiting for a vocal track; it's one of the few cuts on "II" one feels a band could do justice to. "Waterfalls" is a classic McCartney ballad, though it tends to Dan Fogelberg turgidity. You get 38 minutes of clean demos on "McCartney II," but it's not worth the price of admission. It's a miserable mistake a man getting $40-$50 million dollars a year can afford to make.

On "Trilogy" (Warner Brothers 3FFS2300), you get 106 minutes of Francis Albert Sinatra. The set is broken up into three volumes: "The Past" (older tunes from Broadway and Tin Pan Alley); "The Present" songs from Billy Joel, George Harrison, Neil Diamond and others) and "The Future" (an overblown, incredibly schmaltzy oratorio titled "Reflections on the Future in Three Tenses" by Gordon Jenkins). This last one's almost as indescribably ridiculous as the "Tenement Symphony in Three flats" from the Marx Brothers' "Big Store."

The problems of "Trilogy" are the problems of Sinatra himself. At 65, he must work within an increasingly constrained range of darker hues; he tends to flatness and has trouble with both the dynamics of the lower range and substance of the high end. One is willing to give Sinatra a lot of leeway -- no pop vocalist ever matched the superb thrust he gave to his lyrics -- but past, present and future selections all tend to an uncharacteristic general delivery and declamatory style.

Thus, while "The Way You Are" and "Song Sung Blue" get unusually swinging arrangements by Don Costa, Sinatra lags behind the orchestra's drive. Only two songs from the present (Peter Allen and Carol Bayer Sager's "You and Me, We Wanted It All" and Marilyn and Alan Bergman's "Summer Me, Winter Me") are appropriately sophisticated ballads in the Sinatra tradition. But then, Sinatra has another long tradition of missing the boat on contemporary material.

The most consistent album is "The Past," and Sinatra is at his best when he repeats his. There are a few overly maudlin realizations -- "My Shining Hour," The Song Is You" -- but with guys named Berlin, Porter, Gershwin, Kern, Mercer, Arlen and Hammerstein throwing the pitches, you're bound to have more hits than misses.

These expensive and overwraught albums should not be seen as a cap to Sinatra's career. As he has done to often in the past with failed projects, Sinatra will survive "Trilogy." His best records are in the past; that's why they're called classics.