BY JOEL MAKOWER

Which would you buy?

For those with even a scintilla of eco-consciousness, the answer is a no-brainer: the "greener" one is preferable.

So, given that public-opinion surveys report that roughly three Americans in four call themselves environmentalists, and that marketing studies tell us that roughly seven in 10 consumers would gladly choose the greener product over its less-green counterpart, why has green consumerism remained a largely marginal aspect of shopping?

The chasm between green concern and green consumerism is, for me, one of the more curious and frustrating aspects of the environmental movement. For all the activism and consciousness-raising, for all the thinking locally and acting globally, the overwhelming majority of consumers haven't exactly demanded greener products. Only a relative handful of consumers regularly go out of their way to make environmentally preferable buying choices.

It seems the so-called green consumer movement was one of those well-intended passing fancies, a testimony to Americans' never-ending quest for simple, quick, and efficient solutions to complex problems. What happened? Here are five reasons why the environment has failed to become a mainstream market force:

1. There's no mandate.

Though polls tell us that most consumers prefer greener products, the polls are misleading: they fail to ask the right questions. If you pose a question as a green versus ungreen choice, as I did at the beginning of this column, the answer is obvious: everyone prefers the greener choice.

But if you probe deeper into consumer attitudes, the real answer is that consumers will choose the greener product-IF it doesn't cost more, comes from a brand they know and trust, can be purchased at stores where they already shop, doesn't require a significant change of habits to use, and has at least the same level of quality, performance, and endurance as the less-green alternative.

That's a high hurdle for any product. No wonder mainstream consumers turned off to environmentally conscious shopping.

2. The public is dazed and confused.

Shopping with Mother Earth in mind is no mean feat, even for the most savvy of shoppers. After all, understanding the environmental implications of something as simple as paper versus plastic shopping bags requiresdigesting a fair amount of science, some of which is inconclusive, contradictory, or simply arguable. Both, after all, come from limited, declining resources, can be made from recycled material and can be recycled.

Which is better? Even the scientists don't agree. (Of course, the greenest bag is the reusable organic cotton or hemp bag you use thousands of times before it must be turned into compost, but that notion rarely gets considered at the end of a checkout line.)

3. People lack perspective.

Similarly, most people don't have a clue about the relative environmental impacts of the things they do every day. For example, a good many self-described green consumers don't seem to find irony in jumping into their poorly tuned, gas-guzzling sport-utility vehicles with a cold engine and under-inflated tires to drive a couple miles out of their way in bumper-to-bumper traffic in order to buy their favorite brand of recycled paper towels.

Will buying the right laundry detergent or ice cream make the world safe for gas-powered lawn mowers, leaf blowers, and chain saws? You make the call.

The whole notion of green consumerism unwittingly contributes to this lack of perspective. It implies that greener purchases can help "save the earth." The dirty little secret of green consumerism is that we're not likely to shop our way to environmental health.

4. Companies making greener products are afraid to speak up.

With good reason. Those early purveyors of "degradable trash bags" and "ozone-friendly aerosols" got their wrists slapped, so marketers are understandably gun-shy on making environmental claims, particularly those that are scientifically debatable. And most companies aren't environmentally pure, so to call attention to one's green goods risks calling attention to one's ecological skeletons. Better to keep one's corporate mouth shut, right?

5. Green benefits aren't always evident.

As the Levi's example demonstrates, many environmental initiatives companies take don't show up on product labels.

For example, Anheuser-Busch saves millions of pounds of aluminum a year by shaving 1/8" off the diameter of its beer cans, though they don't put eco-labels on cans of Busch and Bud. Nonetheless, they're having a significant impact when you consider the energy and resource inputs of aluminum and the energy savings from trucking lighter-weight cans. It's certainly a greater environmental contribution than that of consumers pondering "paper versus plastic."

For now, it seems green consumerism is destined to be limited to the roughly 10 to 12 percent of the marketplace that pollsters tell us are willing to regularly seek out and buy green products, regardless of how much more they cost or what lengths one must go to find them.

Despite its frustrations, green consumerism remains a powerful, largely untapped tool for environmental change. The fact is that every time we open our wallets, we cast a vote for or against the environment.

And the marketplace isn't a democracy: It doesn't take 51 percent voting in one direction to affect change. A relatively small number of consumers can be a potent force. The model works. We just need to make it work harder.