Phil Marineau's wardrobe is "business appropriate" - turn-of-the-millennium jargon for casual office wear. Since Levi Strauss hired him from PepsiCo five months ago to run the company synonymous with denim, his collection of jeans has grown from two to 20 pairs, and he has yet to be spotted in a suit and tie.

"I'd taken a couple of companies dress-down before I came here," he says. "It's one of the easiest and most popular things you can do as a boss." His task at Levi, however, will be more difficult to smarten up a brand that has worn through at the knees and frayed at the seams.

In the past three years, Levi's sales have slumped from $7.1 billion (€7.3 billion) to $5.1 billion, poor distribution has alienated retailers, and the once iconic brand is now seen by younger shoppers as "something you might put on if you were going to mend a leaking toilet", says Mr Kurt Barnard, retail consultant.

In the past decade, its market share has been cut in half, as VF Corporation's Wrangler and Lee brands, own-label offerings from Gap and new entrants such as Tommy Hilfiger encroached on a market once dominated by Levi's 501 line.

As Levi is a private company, controlled by the descendants of its founder, Mr Marineau does not have a stock price to worry about, nor does he have the comfort of a strong balance sheet. He arrived soon after Levi had breached its debt covenants, and has spent his first months renegotiating its bank loans, prompting rating agency downgrades and forcing Levi to use its prized trademark to secure new financing.

"We can restore Levi. I think it can be a great, financially strong company again," he says. The 53-year-old forecasts that within two or three years, sales growth will return, and cashflow haemorrhages resulting from costly restructurings will be stanched sooner.

His plan is to restore financial disciplines without further disruptive restructurings, to tighten up Levi's replenishment systems so retailers' shelves are not left empty, and finally to rethink Levi's portrayal of its brand.

The last goal may be the hardest to achieve. Mr Martyn Straw, Interbrand consultancy president, says: "Levi has not kept up with the brand's image of authenticity and rugged individualism."

He argues that there are two aspects to any brand - its latent, long-term identity, and the way it is represented in the market.

Of the first, he says: "The embers are still quite bright." As for market representation: "The brand is absolutely nowhere now."

Sitting in Levi's showroom in Manhattan's garment district, Mr Marineau says: "Levi jeans are a huge mass brand. Don't make them just for some 18-year-old with a ring through his or her nose. I want some 50-year-old fat guy sitting in a conference room in New York to wear them too."

Levi is launching Engineered Jeans, an aggressive modern range with skewed seams and new, softer material, which it hopes will restore the brand's credibility with fashion-conscious 15-24 year olds and create a `halo effect' for the entire brand. But Mr Marineu believes that Levi faltered because it veered too far towards fashion, and says its branding efforts should concentrate on the strengths of its core five-pocket product line.

"The advertising focused too much on being hip and cool, not on having a great product and then wrapping it in an attitude of youthfulness and sexiness," he says. "We are not selling attitude here, we are selling product."

His comments are heretical to some branding consultants, and Mr Straw is taken aback by Mr Marineau's plans. "Emphasising the quality of the jeans will absolutely take the brand the wrong way. The quality of Levi's product is good, but so is everybody else's. People buy jeans for attitude."

Instead, Mr Straw argues that Mr Marineau's priority should be to redefine what the Levi brand stands for, even if that means applying its brand to other product lines such as fragrances, as Ralph Lauren and others have done. Mr Marineau's controversial branding ideas stem from his experience as head of Pepsi-Cola North America. On joining the cola company, he swiftly scrapped its "generation next" ads because he felt their focus on young customers was too narrow, and introduced the highly rated "joy of cola" campaign. "We went back to what Pepsi stood for the product. Taste. A symbol of freedom of personal choice."

Just as he is seeking to use Engineered Jeans to bring some cachet back to Levi's broader wardrobe, so he created a buzz around Pepsi with the launch of Pepsi One, its low-calorie drink. However, the fizz has gone out of Pepsi One in recent months and Mr Marineau concedes: "Getting your young to survive is really, really hard."

Mr Marineau earned his reputation as a brand builder during his 23 years with Quaker Oats. He took charge of Gatorade, an obscure sports drink, in 1984 and by the time he left Quaker in 1996 he had expanded it to a $1.2 billion business.

Mr Marineau marked his arrival at Levi by holding one-to-one meetings with many of its employees "so people could really tell me what they feel".

But Mr Marineau has already demonstrated an ability to go against the flow. As other apparel companies were pouring millions into e-commerce last year, he ceased sales over the Levi website because the effort was costing too much money.

The Internet will be one of the great marketing tools of the next 20 years, he predicts, with opportunities for marketing customised products individually, but "I wouldn't do a banner ad if my life depended on it".

Mr Marineau's is confident he will last longer at Levi Strauss than some of his predecessors. Having moved his family from midtown Manhattan to San Francisco he says: "I'm never moving again. I'll finish my career here."