MAPLEWOOD, Minn. - Scotchgard is back.

The familiar plaid aerosol can never really disappeared from the shelves. But Scotchgard's journey back to the market has been rocky -- and the stain repellent is still missing from the furniture upholstery industry. 3M's venerable line of fabric protectants -- so ubiquitous that ``Scotchgard'' became a verb -- has been struggling since the Environmental Protection Agency pressed 3M in 2000 to stop using the chemistry behind the spray.

3M, based in Maplewood, has lost two-thirds of its former $300 million-a-year Scotchgard business and hopes to rebuild it to $500 million by 2008. Finally finished with its phase-out and armed with a new formula it says is safe and better than ever, 3M is launching major Scotchgard replacements this summer, marketing them like new products.

Clothing pretreated with Scotchgard will reappear in stores this summer, with the debut of the new Scotchgard aerosol spray for consumers. A new ad campaign is slated for this winter. And Scotchgard is headed for places it hasn't been before, like eyeglass lenses and paint.

But it can't happen fast enough for Wall Street, which wants to know what's taking so long even as the EPA sharpens scrutiny of the chemical family behind both Scotchgards, old and new.

And there's some confusion among Scotchgard customers.

``I thought they discontinued this stuff,'' said a woman picking up a can of the new Scotchgard at 3M's recent shareholders meeting.

For nearly 50 years 3M has marketed Scotchgard, a bedrock brand that evolved after some rubber particles a chemist cooked up in 1953 accidentally splattered on an assistant's tennis shoe. The stubborn goo wouldn't come off.

Scotchgard grew to encompass some 100 products -- most based on a key chemical known for its remarkable ability to repel nearly anything people threw at it. The chemical breaks down into perfluorooctane sulfonate, or PFOS, a manmade substance that is part of a family of chemicals characterized by chains of carbon atoms of various lengths bonded to fluorine atoms, yielding armorlike compounds. PFOS has a chain of eight carbon atoms, or C8.

But PFOS began showing up everywhere: in polar bears, dolphins, baby eagles, tap water and human blood. So did its eight-carbon cousin perfluorooctanoic acid, or PFOA, which 3M sold to other companies such as DuPont for use in products like Teflon.

Linked to cancer

The two manmade perfluorochemicals don't decompose in nature. They kill laboratory rats at high doses, and there are potential links to tissue problems, developmental delays and some forms of cancer.

3M knew much of this because it had studied the chemicals for decades. It insists that at typical low levels found in Scotchgard and elsewhere the chemicals posed no health or environmental risk.

A former employee has sued the company over exposure to perflourochemicals at the company's Decatur, Ala., plant. 3M says the case has no merit.

Yet accounts differ as to whether 3M voluntarily phased out the problematic C8 chemistry or was pressured by the EPA after the company shared its data in late 1999. The EPA concluded PFOS was toxic. Either way, the phase-out was largely completed in December, although 3M still makes small amounts of PFOA for its own use in Germany. 3M, which still monitors chemical plants in Cottage Grove, Minn.; Decatur; and Antwerp, Belgium, insists there are no risks for employees who handled or were exposed to the chemicals.

Markets suffered

The phase-out went unnoticed by most consumers as 3M rapidly substituted another, less effective spray for consumers. But the move stunned industrial clients -- the bulk of Scotchgard's business. 3M's chemists scrambled to reformulate Scotchgard for all its markets, but the lags have hurt.

The replacement aerosol-can Scotchgard that 3M first distributed to stores didn't work as well as the original. It was based on non-perfluoro chemistry and worked on water but not grease. Nothing repels like perfluorochemicals, 3M concluded. The challenge was to find safe ones.

3M settled on perfluorobutane sulfonate, or PFBS, a four-carbon cousin of the chemical in the old Scotchgard, as the building block for Scotchgard's new generation.

``For providing protection you almost can't do it without a fluoro-chemical, short of plastic slipcovers,'' said Michael Harnetty, vice president of 3M's protective materials division.

The new C4-based Scotchgard is completely safe, 3M says. The company adds that it has worked closely with the EPA and has performed more than 40 studies, which are confidential. The EPA won't release them.