Joe Montana went Christmas shopping once this month. His girlfriend bought the presents and he hid behind the clothes racks.

" 'I hate to interrupt you, but,' " Montana said with a grin. "Those are the beginning words. 'I hate to interrupt you, but . . . ' " The grin widens. Joe Montana has a spectacular grin. When he grins, he looks as though some rain-chilled New Yorker, imagining California, invented him.

Nobody north of the Western White House really looks like this. He has wide blue eyes, straight teeth and a strong, angular jawbone. He has golden hair just unkempt enough to curl out from under his helmet. He has a deep-cleft chin, like Kirk Douglas. A face like that, you're in trouble even if your name is Fred Smith and you sell real estate.

"Once you start signing (autographs), then people start seeing you sign, so you hide behind the corner," Montana said. "It's not that I don't like it. But you can't concentrate on what you're trying to do . . . During this time of year, it's really difficult, especially when you're having success, like our team is, 'cause I like doing the simple things with her, like going to the grocery store."

Joe Montana, who by certain statistical measures is among the best quarterbacks in the history of the NFL, has a hard time going to the grocery store in San Francisco. Just his name, his wonderful, loping gunslinger name, might have been enough to make the city fall in love with him. Dwight Clark, the 49ers' wide receiver who has become Montana's best friend, decided long before he met him that Joe Montana (it's Italian, changed from "Montagna" somewhere along the ancestral line) was the greatest stage name he had ever heard.

But then there was Montana's face, grinning out from all those magazine covers the week San Francisco won the 1981 Super Bowl, or receiving a suitably publicized kiss from the 1983 Miss Northern California National Teen-ager, or mugging innocently into the television camera for his razor commercial. There was the way he always managed to look a little rumpled and overwhelmed by all the attention he was getting, as though someone had just dragged him off the field to address Congress. There was his ardently followed marriage to and divorce from the comely and unabashed Cass Montana, whose name was nearly as terrific as his.

And there was also -- not to lose track of priorities -- his record.

By the time the 49ers finished off the Los Angeles Rams, 19-16, two weeks ago for their 15th victory of the season, Joe Montana had settled in as the highest-rated passer lifetime in the history of the NFL. This year, as the 49ers begin their final push toward the Palo Alto Super Bowl that will be held practically next door to their Redwood City training camp, he has completed 279 of 432 passes, 28 for touchdowns and with only 10 interceptions going into Saturday's playoff game against the New York Giants.

His quarterback ranking this season is 102.9, making him the NFC leader; in all the NFL, only Miami's 108.9-rated Dan Marino is higher. Montana appears, both from scuttlebutt and public comment, to elicit only praise from teammates, who describe him as a kind of luminous presence on the field, all confidence and relaxation at the most frantic of moments.

"He doesn't have to say anything," said Clark. "When it starts getting real intense, it's like he goes the opposite way. He just kind of mellows out in the huddle."

"He doesn't react to the pressure like a lot of people would," said tackle Keith Fahnhorst. "He's not as flashy as some guys might be, but it's just because he's so consistent."

And for all the less-than-adulatory fans who have decided Montana is a dazzlingly accurate short passer who can't quite manage the dramatic long throws, he has begun to shine even at that. After the 49ers clinched the NFC Western Divison title last month, Coach Bill Walsh began experimenting with his celebrated ball-control passing game, an offense that perfectly suits Montana's precision and scrambling ability.

Part of Walsh's experiment was plotting deep pass plays, and Montana not only delivered, but did it with memorable timing. In the 49ers' victory over Minnesota two weeks ago, he threw a 59-yard touchdown pass to swift wide receiver Renaldo Nehemiah.

"It's always been that I couldn't reach him," Montana says, mimicking the way people have dismissed his passing strength. "But over the past couple of weeks, I've found out more or less the opposite. On the practice field, you don't get the same reaction -- you don't get the guys running the same speed, you don't have the feel of the people around you -- so it's completely different, and it's something I haven't done. Even at Notre Dame, I didn't do a lot of it, only because the offense was built around the shorter-type stuff."

He is draped over a straight-backed chair, one long leg up on a cluttered desk at the 49ers' headquarters. He is friendly, a little uneasy and improbably shy; when he talks about meeting his girlfriend last year (they appeared in the same commercial and the director told him to loosen up, so she pinched Montana), he blushes to his hairline.

"It did the job," he said. "The hardest part was, initially, when you get there, you have to shave in front of the camera. Shaving's difficult enough as it is. In front of 15-20 people that you've never seen before, and a camera two feet in front of your face" -- Montana laughs -- "that was hard."

He looks, as he always does, too skinny to be a football player: 6 feet 2 and 195 pounds, the press guide says, but you'd never believe it gazing out at that rangy body on the practice field. Basketball nearly wooed him away years ago; Montana was an all-state high school basketball player and played so well that North Carolina State offered him a basketball scholarship. He loved the sport, loved especially the way practice was almost as fast and exhilarating as the game -- no elaborate offensive plays to study into the night, no drawn-out, slow-motion practice exercises on chilly fields.

"But being 6-2 and white, and making it in the NBA . . . ," Montana said with a smile. "I really enjoyed practicing on the whole basketball. It was more enjoyable. But with game time, it was football. It was so much more fun than anything else."

Montana is a Pennsylvania boy, raised in the town of Monongahela, which lies in the steel and coal valleys just south of Pittsburgh. "Joe Namath, Johnny Unitas, they're all from around here," said his mother, Theresa Montana. When Notre Dame offered him a football scholarship, Montana took it. "I grew up hearing about Notre Dame," he said.

He finished at Notre Dame with a reputation for yanking his team back from the edges of cliffs -- 20- and 22-point third-quarter deficits turned to victory in the final moments of the game. But the pro scouts did not think he had the look of a particularly hot prospect.

The scouts talked of an erratic player with a weak throwing arm, Walsh remembered, but the 49ers saw potential in Montana's passionate play. He was a third-round draft choice of the 49ers in 1979, and in 1980, after a year as second string behind Steve DeBerg, Montana became a starter in Walsh's second season with the team.

One year later, San Francisco won its first Super Bowl. Larry Muno, Montana's agent, still keeps on his office wall a picture frame holding the week's covers of Time, Newsweek, Sports Illustrated, Pro and Sport -- each one featuring his client, who instantly became a hot property.

Montana sold blue jeans, tennis shoes, gasoline additives, watches, home computers, boots, autos and sporting goods. He analyzed football games on the "Joe Montana Show," starred in feature pieces on the evening news, appeared at charity dinners and banquets. The town of Monongahela invited him back for his own civic holiday, complete with a homecoming parade that featured the high school marching band and police cars from eight nearby towns.

Montana, who says that he copes with 800 pounds of galloping defensive linemen by momentarily declining to see them, had to give a speech for Joe Montana Day and says it was the most frightening thing he has ever done. "Sweating," he says. "Cold chills . . . I find it difficult to -- I don't know -- express myself in front of groups. But the hardest thing is expressing yourself in front of a group of people you know. It makes it 10 times as hard."

He so badly wanted to do it right, he said, and he wasn't sure how. He wanted to be articulate, but he wanted them to know that he hadn't become awful and swell-headed just because he was famous. "I know that some of the people who were there probably still thought that," he says.

Nobody in San Francisco seems to think Montana is awful or swell-headed, despite his salary, which has been reported at million and up yearly through 1989, and the endorsement income, which Muno discreetly describes as "in excess of $1 million."

There are complaints once in a while that although he may be a great quarterback, he's not flamboyant enough to be much fun. Montana's red Ferrari appears to be the limit of his conspicuous consumption; he lives, in as much tranquility as possible, in a San Francisco apartment shared by his girlfriend, Jennifer Wallace, a model and actress he plans to marry next year.

Even his divorce in 1982, which was followed by a lot of people eager for some hint of Montana nastiness, was settled relatively peacefully. Cass Montana limited her public comment afterward to some philosophical reflections about the perils of celebrity. "Fortune is fun," she said, "but fame -- fame can be devastating to a marriage."

And even though Montana still looks as though he can't imagine why people keep expecting him to say and do something momentous besides throwing a football better than anyone else, he is not quite that disturbed about fame. "I don't mind," he says. "I love it most of the time. I think it's -- I don't know, maybe they play athletes up sometimes too much. I guess it's role models for kids, which I guess I agree with and like." He and Jennifer Wallace will have children of their own, he says. He says he can't wait.