Imagine that you want to start using a new raw material called glop to produce your packages. Your customers are clamoring for it.

The technology is in place, the market is there. The only problem is that you can't find a large, steady supply of glop. Do you move forward with your investment?

Or, imagine that you have a source of glop. You'd like to sell it to someone who can use it; otherwise, glop is just garbage -- and costly since you've got to find a place to dump it or burn it.

There are a few potential buyers who are using glop, but they are scattered, and there aren't any brokers through which to sell it. Do you invest in equipment that will turn glop into a usable material or simply dispose of it?

In recent years, recycled plastic has become in effect a new raw material struggling to make the transition from garbage to valuable commodity. The plastic to be recycled and the desire to use it are both there. But the absence of a system to tie it all together stands in the way of wide-scale plastics recycling, say environmentalists, solid waste handlers and recycling experts.

On the supply side, the nation's landfills provide plenty of potentially recyclable material. Although plastic makes up only 8 percent of the municipal solid waste stream by weight, by volume it accounts for 19.9 percent.

Not only is the potential supply of recyclable plastic large, consumers have proven willing to help sort it out for recycling -- sometimes almost too willing.

When Montgomery County started a pilot program in Rockville to collect used milk jugs and soda bottles, residents were so eager to help that they threw in piles of other plastics besides, complicating the task for recyclers. And Giant Food was forced to close four parking lot recycling centers earlier this year because the overwhelming response to the invitation to deposit cans and plastic bottles spilled into the lots.

On the demand end are manufacturers like Lever Brothers Co. and Procter & Gamble Co. that want to use recycled plastic in their packaging. Procter & Gamble is making bottles for Tide, Cheer, Era, Dash and Downy with at least 25 percent recycled product, and Spic 'n Span Pine liquid cleaner bottles entirely from recycled plastic. Lever Brothers is including recycled plastic in bottles of Wisk and All liquid detergents and Snuggle liquid fabric softener.

What is missing -- or at least only beginning to be forged -- is solid links between supply and demand.

The markets for other commodities -- those that carry wheat from the farm in North Dakota to the shelf of the Safeway, for instance -- are so well-established that it's easy to lose sight of how elaborate they are and difficult to build.

Other materials that can be recycled, including aluminum, glass and paper, have faced some of the same problems establishing themselves as new commodities in the marketplace. But the case of plastic is particularly complicated.

"It's not just a matter of getting the supply, collecting the bottles and shipping it to recyclers," said Jeanne Wirka, policy analyst with Environmental Action Inc., a Washington-based environmental advocacy group. "It's getting a high enough quality of supply to the manufacturers that they can use it."

Waste managers have not traditionally thought of themselves as suppliers of raw materials, Wirka said. "In garbage collection," she said, "you just collected the stuff."

Plastic is the generic name for a number of different resins. Separated, some are valuable. Mixed together, they aren't worth much. Nor can pigment be removed from plastic, which imposes additional limits on the reuse of colored plastic.

All these factors add to the costs of collecting and recycling. "The plastics industry likes to say it is the second most valuable product in the waste stream, next to aluminum," said Esther R. Bowring, a recycling director for Montgomery County. But that value is offset by the cost of collecting it "because it's 90 percent air," Bowring said.

Nonetheless, the links in the recycling chain are being built. In the last two years, two major joint ventures have been announced that include long-term contracts between companies that collect used plastic and companies that plan to recycle plastic for their own use or for sale. Such arrangements are helping to move the market for recycled plastic away from a somewhat ad hoc spot market to something more regular and reliable.

Wellman Inc., the nation's largest recycler of plastic soft drink bottles, and solid waste giant Browning-Ferris Industries announced a joint venture last year under which BFI will collect plastic from curbside recycling programs to supply Wellman.

In an earlier deal, Du Pont Co. and Waste Management Inc. entered into a joint venture that operates recycling plants in Chicago and Philadelphia, which together can produce 80 million pounds of recycled plastic a year.

"If we don't have a market, we don't have a business," said Frank Aronhalt, director of environmental affairs for Du Pont. "We view the recovery of these materials as an alternate source of feedstocks either for things Du Pont makes or for our customers."

Du Pont, a long-term recycler of industrial plastic waste, has found that recycling post-consumer plastics can be a tougher task. In addition to sorting plastics, much of which is done by hand now, "you've got to take off the labels. You've got to take off aluminum caps. You've got to get it to a pure state," which involves removing food residue, paper and glue, said Aronhalt.

But "there are some concepts the packaging industry is looking at that would encourage product design that would be more easily recyclable," he said.

Wellman started recycling plastic collected from consumers in 1979, long before the current interest developed. Its initial supply came from nine states that had mandatory deposit laws, which helped guarantee a steady supply.

"There are only two problems in curbside recycling in our view -- the collection and the sorting infrastructure to get the recyclables out of the waste stream," said Dennis M. Sabourin, vice president of Wellman, which uses recycled plastic to produce fibers and other products.

Wellman recently acquired a a solid waste management company that has the rights to a Rube Goldberg-like materials recovery technology developed in West Germany. The process sorts through and separates aluminum, steel, glass and plastic. Montgomery County is building a recycling facility using that technology.

The two most widely collected post-consumer plastics are polyethylene terephthalate, or PET, soft drink bottles and high density polyethylene, or HDPE, milk jugs. But even after those products are separated from other plastics, there may be additional complications. For instance, the black base cups on many large soda bottles are made of HDPE, which must be separated from the PET. But the HDPE from the base cups can't be mixed with the milk jugs either, both because of its color and because it is made through a different process, said Sabourin.

The plastics industry stamps codes on containers that indicate the resin type and help with the sorting process. Gravity can help with the process too, since some types of plastic sink in a solution in which others float.

In general, however, the technology will probably have to develop further before recycled plastics become widespread, according to many in the industry.

"The plastics industry is just coming into its own" in terms of recycling, said Bob Davis, BFI vice president for recycling. The industry is "either going to get very deeply involved in recycling or they're going to have it legislated," he said.

When most "major plastic companies start to incorporate post-consumer recycled material in their products, I think you're going to see the market mature very fast," Davis said.

In the meantime, however, despite a growing interest in plastics recycling, it hasn't exactly swept the country. Approximately 292 community recycling programs currently accept post-consumer plastics, said Terry Grogan, the Environmental Protection Agency's chief of the solid waste recycling section.

"We know of something on the order of 1,500 curbside recycling programs in general," he said. "If you compare those numbers, clearly a lot of communities are collecting recyclables that are not dealing with plastic."