WHAT KIND OF person lives to be 85 years old but keeps the mind and energy of a 20-year-old?

He that hath clean hands and pure heart.Ask A.W. "Mickey" Hart. He knows. He wrote the song.

It's difficult - no, it's almost impossible - to grow up Mormon in Utah and never hear a tune composed by Hart. "They Found Him in the Temple," "If Christ Should Come Tomorrow," "I Walked in God's Garden." In a recent poll, Hart was the only composer to land five songs on the list of "all-time-great religious songs." He's written hundreds of the things, literally. And currently he's putting together a series of songbooks that are chock-full of fresh material for children.

Did I mention the man is 85?

"Somebody once asked me to name the best song I ever wrote," he says. "I said, `The one I'm going to write next.' I work on four or five songs at a time. And I learn something each time - some twist or turn. I marvel at it."

Raised in hard-scrabble Pocatello, Hart was the only one of seven siblings who was never given a musical instrument as a child. His parents felt he lacked the talent. But when a local piano teacher ran up a $6 debt with his father, Hart talked his dad into letting him take it out in piano lessons at the going rate of 35 cents.

Not long after, Hart began studying with the best teacher in town. She told him he'd have to practice three hours a day for three years to get to concert level. Hart practiced five hours a day for three months and got there.

"I tried to practice eight hours a day for awhile," he says, "but my body couldn't take it."

Today, sitting at the grand piano in his living room, Mickey Hart gives a crash course in songwriting that would burn out the brain cells of most college kids. He tells how songs in the '40s all seemed to begin with the interval of a third, he explains how Berlin composed, how Gershwin went at it.

"If I had only three hours to compose a song," he says, "I'd spend the first hour on the first three measures. Those first three measures tell you which way the song will go, the way the twig is bent. And the little tricks of the trade make it work.

"I'm like a guy on a motorcycle. If I don't get a big enough run at the hill, I'm not going to make it over. As a songwriter you have to lean back and feel that wheel churning under you at all times."

And the lyrics?

"You know," he says, "I used to say, `Lord, why don't you send me someone who writes words?' But he never did. And I'm grateful, because I learned to write my own."

As with most musicians, Hart has had a career with more than a few dips and turns. He wrote the song "There Is a Shanty in Old Shanty Town," but had the song pirated from him by an unscrupulous Hollywood producer.

He did gigs in California, jamming with Benny Goodman and Glen Miller. At one point Miller wanted Hart to join his band and meet him at the Black Hawk Cafe in Chicago, but the thought of rough-and-tumble Chicago left the young songwriter uneasy.

He returned to the West to his roots. His home.

Miller's loss, of course, was Utah's gain. Mickey Hart's songs, musicals, anthems, children's songs, jingles and hymns have become as much a part of Mormon culture as Seagull Monument.

"If I write a song and it's good, I didn't write it," he explains, "it already existed. If I write a song that's no good, then I know I wrote it."

Hart has never sought the limelight. And for such reasons he's probably ended up with less than he deserved. But there's still time for him to get the recognition if he wants it. Right now, for example, he's working on new number. The opening line is very telling: