It’s noon on a Tuesday in late April, and the Levi Strauss in downtown San Francisco is nearly empty. There’d be echoes in the four-story flagship store on Post Street if not for the techno-jazz pounding on all floors. As smiling assistants fold T-shirts and straighten 501s, a cargo-style elevator creeps up and down the middle of the building. An old-fashioned sign, picturing a man in a cowboy hat and coveralls, reads "Levi’s fits ’em all."

Maybe so. But these days, not enough customers are buying.

Once upon a time, Levi’s and blue jeans were synonymous. James Dean looked oh so cool in them. Marilyn Monroe looked...real good. Almost since its founding 150 years ago, the company has been an American icon. But tastes change. For a time, nothing could come between teenage girls and their Calvins. Twentysomethings started going to malls and haunting The Gap. And by the mid-1990s, Levi’s had missed the baggy pant craze that overtook American high schools. In 1996, Levi’s sales peaked at $7.1 billion. Last year, they fell to $4.1 billion, a six-year low. The competition has nibbled away at Levi’s jeans market share, which has tumbled to about 12 percent from 18.7 percent in 1997.

Since the peak, Levi’s, which also makes casual Dockers and higher-end Slates clothing lines, has seen its customer base pulled apart. On the high end of the market, fickle fashionistas are eschewing Levi’s in favor of boutique brands such as Blue Cult, Juicy and Seven. On the low end, moms are buying Lee and Wrangler for their kids because they’re affordable (on average $10 less than Levi’s Red Tab) and because they find these brands at the superstores they prefer: BJ’s, Sam’s Club, Target, T.J. Maxx and so on.

David Bergen, Levi’s senior vice president and CIO, says his company is caught in the "jaws of death." "We’re getting squeezed," he says in his office in Levi’s Plaza, which has a startling view of San Francisco Bay and is about a 30-minute walk away from the Post Street store. But Levi’s thinks it may have found a way to cheat a retail demise.

Wal-Mart.

Wal-Mart, the world’s largest retailer, is where moms go to stock up on Max and Maddy’s school supplies, their juice boxes and, of course, their jeans. So if you want the kids, and the rest of their families, you need to sell at Wal-Mart.

And you need a new product for this new customer. This month, Levi’s is introducing its new, less expensive Signature jeans line. (The jeans, for men, women and children, sell for around $23. They have fewer detail finishes than Levi’s other lines. They don’t have the company’s trademark red tab or stitching on the pocket.) Of course, there’s something in it for Wal-Mart. The company, already the largest clothing retailer in the world, wants more affluent customers. To lure them in, it needs big brands. Acknowledging that the company’s customers come from a "cross-section of income levels and lifestyles," Wal-Mart Senior Vice President Lois Mikita says the company "continues to tailor its selection to meet the needs of those customers."