When you're a rock 'n' roll star just turned 27 and sales of your last album have just cracked the 11 million mark - making it the fastest selling album in history and making you $6.5 million richer than you are 15 months ago - what can you do to top yourself?

If your name is Peter Frampton, you spend several months in a New York recording studio, cross your fingers, take a deep breath, release a modest little record called "I'm In You" and hope for the best.

You can also decide to become a movie star by signing on to play the lead role in the movie version of "Sgt. Pepper's Lonely Heart Club Band" - the best-selling rock album ever until yours surpassed it.

But let's face it: Peter Frampton is in an impossible situation. The unprecedented success of "Frampton Comes Alive!," the live, double record set that produced three hit singles and turned Frampton into pop music's biggest new star in years, has created expectations he can't possibly be expected to fulfill. Frampton is not, after all, a genius.

In the late '70s, though, you don't have to be a genius to be as popular as The Beatles or Stevie Wonder. All you have to do is deliver the sound the pop public seems to find irresistible - a kind of pretty, soft-edged rock 'n' roll that, as the Eagles and Fleetwood Mac have also discovered, may be the only thing on which the heavy meal crowd and their older brothers and sisters can agree.

Frampton didn't arrive at the style overnight. He spent several years in a lighweight British Top-40 group called The Herd and then moved on to a heavy metal quartet known as Humbl Pie before embarking on a solo career five years ago. All during that time he tried to strike a balance between his melodic, romantic instincts and what was demanded of him as a rock guitarist - to be loud and brash.

When he finally found the right blend, he had a lot to go with it: It's not for nothing that Frampton's nickname in rock circles has for years been "The Face." He's sexy in a pretty, wholesome way and looks as good on the cover of Time, After Dark or Rolling Stone as he does from a concert stage, his shirt open to the waist and his lean, trim body and curly hair moving in time to the music.

So it scarcely matters now that "I'm In Your is the blandest and most timid album Frampton has ever made. "The Face" is a phenomenon now, set to star in the movie version of "Sgt. Pepper's Lonely Heart Club Band" just as soon as he finishes his next concert tour. All those years on the road with Frampton's Camel, playing second bill to heavy metal bands and country rockers alike, have finally paid off.

If proof is needed that Frampton has arrived, it can be found on "I'm In YOU," WHERE Mick Jagger sings background vocals on "Tried to Love" and Stevie Wonder plays harmonica on "Rocky's Hot Club," a tribute to Django Reinhardt. They are Frampton's two favorite musicians, and his liner notes indicates it was a real ego boost for him that they had "come along to help in the same night."

Frampton also notes that he was trying not to compete with myself" but that 'even so, subconsciously there was an underlying pressure to 'outdo' the last album." He's avoided that problem, though, and in a very nifty way: by paying tribute to the musicians whose music he most appreciates.

But that inevitably means that on much of the album Frampton sounds like a watered-down version of someone else. On Wonder's "Signed, Sealed, Delivered (I'm Yours)" he is overwhelmed by Mike Finnegan's funky background vocals, and though he manages to duplicate the Little Feat piano and slide guitar sound on 'Won't You Be My Friend," he again falls down on the vocals ' not to mention the lyrics.

The main weakness of "I'm In You," in fact, is Frampton's reluctance to rely on what is probably his greatest gift - a sense of melody that is exceeded only by Wonder's and perhaps Elton John's and Paul McCartney's. There are hints of Frampton's true musical character on the title song, just released as a single, and "St. Thomas (Don't You Know How I Feel)," but it emerges clearly only with "You Don't Have to Worry."

Here, in a number that best demonstrates the essentials of his style, Frampton walks the delicate tightrope between the gutsy and the delicate. His lead guitar is strong - not quite as strong as it will later be on a cooking version of Jr. Walker's "Roadrunner," but impressive nonetheless - and is muted by several acoustic rhythm guitars, which take some of the electric edge off and intimate gentle overtones.

Some might call this rock without guts, and in a sense it is. But the kind of compromises Frampton is willing to make - and has made here - are the key to massive success in pop music these days. It's enough to be pretty any more, and it's not enough to have power. You've got to be both.