Wal-Mart Stores Inc. is throwing its weight behind organic products, a move that experts say could have the same lasting effect on environmental practices that Wal-Mart has had on prices by forcing suppliers and competitors to keep up. Putting new items on the shelf this year, from organic cotton baby clothes to ocean fish caught in ways that don't harm the environment, is part of a broader green policy launched last year to meet consumer demand, cut costs for things like energy and packaging and burnish a battered reputation.