In 1795, the French government, desperate to feed its far-ranging army and navy, sponsored a rich prize for anyone who could find a practical way of preserving food.

The glass jar and tin can were the answer and, for almost two centuries, these venerable containers have kept food fresh for armies and households.

Now, after this long run, a new kind of plastic called a barrier resin threatens to push the can and jar off grocers' shelves and out of kitchen cabinets.

First Japanese, and now American, plastic companies have developed multilayer plastic bottles that can withstand oxygen well enough to keep perishable food from spoiling. And unlike metal cans, they can be molded into exotic shapes to entice consumers, opened with a flick of the wrist, popped in the microwave or easily squeezed.

So far, the moves are tentative -- plastic ketchup bottles and jam containers are among the newest of the new plastic products marketed nationwide. But the potential is enormous for plastics companies if they can corner a large chunk of a $35 billion container market. Every year Americans go through an estimated 30 billion food cans and about 70 billion soft drink and beer containers, and an alluring package can make or break some products.

The technological leap is the development of barrier resins, which form a spaghetti-like lattice of polymers too tight for oxygen molecules to squeeze through. Ethylene vinyl alcohol (EVOH) is the most common type of resin. "We see EVOH as a revolution," said Mark Dillon, manager of marketing communications for Norchem Inc.

This Omaha, Neb., company said that it captured most of the three- or four-million-pound EVOH market in this country last year. Taking technology developed by the Japanese firm Kuraray, Norchem has formed Eval Co. of America to produce EVOH in the United States in a plant that will have an annual capacity of 22 million pounds.

"We expect that plant to be sold out," Dillon said.

Campbell Soup is enthusiastically embracing the concept of a new package for its soup. In the last two years, in Hayward, Calif., the company has sold soup packaged in a plastic bowl that is ready to pop in the microwave to heat and then eat. "We're looking for alternatives to the can," said Mel Druin, director of packaging technology.

That would mean a big change at a company that is the third-largest can producer in the world, but Campbell already has learned just how profitable an upscale convenience product can be. The company also is test-marketing frozen soup in a plastic bowl, dubbed Campbell's Soup de Jour.

About 2 1/2 years ago, the company, which owns Swanson Frozen Foods, introduced its Le Menu frozen dinners -- a pricey frozen dinner that can be popped in the microwave. The dinners, which sell for about $2.99 to $4.90, have pulled in $200 million in revenue for the company since their introduction.

Aglow from this convenience-food success, Campbell has set up a $4 million processing facility for plastic prototypes in Moorestown, N.J., according to Druin. Campbell is considering replacing all of its alumninum trays, familiar to generations of TV-dinner eaters, with plastic trays that can be put into microwave or conventional ovens. Campbell now produces more than 500 million aluminum trays and more than 6 billion cans every year.

"We feel more bullish about the plastic tray," said Druin, who added that the company expects microwave ovens to become more popular. "That doesn't mean we're ultimately going to eliminate metal."

Meanwhile, Campbell continues to try to build a better soup bowl. The company is responding to consumer comments that the lid was too hard to remove and is adding flanges to make the bowl full of hot soup easier to handle, Druin said.

Beth Adams, manager of public communications for H. J. Heinz Co., reports that, even though its plastic bottle is slightly more expensive than the glass bottle, it is selling well. Heinz now sells a 28-ounce size nationwide, while its 64-ounce size is available in about half of the country, she said.

Heinz, which says it holds 58 percent of the $500 million ketchup market, wasn't able to sell the 64-ounce size before because the glass bottle was too heavy for the average consumer to heft easily.

"The loser in this is the steel can," said Dewayne Whitehead, manager of the plastic packaging group and vice president of Technomic Inc., a container research firm in Boston. Whitehead predicts that there will be no steel cans in use by 1987, because the new plastics with a high barrier to oxygen can be made with much less energy. Also, he noted that consumers are lured to the more attractive and generally more convenient plastic packages.

Whitehead noted that juice manufacturers have been able to sell more juice by eschewing the old steel can for the plastic "brick packs," small, block-like plastic juice containers of individual servings. "They've gone into vending machines. They've gone into lunch boxes. They've gone into markets they've never seen before," he said.

Most large can and container companies are conducting their own experiments with new materials. American Can Co., based in Greenwich, Conn., introduced its "Gamma" bottle -- which now holds the Heinz ketchup -- and has just announced a new plastic container that can withstand a greater amount of heat. While ketchup and jelly are not reheated after they are poured into a container, many foods are, and their containers must be able to withstand heating tests to the satisfaction of the Food and Drug Administration.

By adding drying agents to its plastic formula, American Can produced its OMNI container, which can withstand high temperatures, according to Barbara Pite, director of sales and marketing for barrier plastic containers. The OMNI container appeared only after scientists developed a proper formula and engineers devised a way to make the containers at a fairly inexpensive rate, she said.

Oxygen-resistant, multilayer containers have a more complex technology than the average metal can. Companies use a special polymer, typically EVOH, to prevent oxygen from leaking into the container and spoiling the food. But the polymer must be surrounded by a layer on either side to give the container form. Two more adhesive layers of plastic are added in between. In the case of the OMNI container, the drying agent also is added.

Plastics manufacturers and researchers agree that a company must make a major investment to switch production from metal cans or glass bottles to plastic containers, and that all the kinks in recycling the material have not been ironed out. But plastics enthusiasts claim that the added consumer appeal, as well as an eventual drop in the price of the oxygen-resistant resin for the barrier layer, will make plastic packaging the wave of the future.

All can manufacturers are not as enthusiastic. "There's a lot of experimenting going on with plastic cans. We have seen nothing that is a viable plastic can," said an official at Crown Cork and Seal Co. in Philadelphia, who added that his company is not investigating plastic containers.

The can industry still remembers well its last major change about 10 years ago in soft drink cans, when it switched from steel to aluminum. Changes also have swept the industry with the introduction of the PET plastic soft drink bottle, with a barrier layer that can keep the fizz in.

Even the metallic coolness of the aluminum can may not be here to stay. Coca-Cola Co. is looking into the possibility of a plastic can, and the material is being researched and fabricated exclusively for Coke by a joint venture of British, Swiss and Sewell, a subsidiary of Dorsey Corp.

But Coke won't talk about its new venture, expect to note that there are still three years left on the exclusive contract and that limited test-marketing may start in a few weeks.

Sales of canned food have slipped 15 percent over the last decade, although they are holding their own this year, he said. Steel only holds about 15 percent of the soft drink can market and less than 1 percent of the beer can market, he added.

The metal can is not taking the plastics push lying down, according to Tom Wilson, senior vice president of product development and promotion for the American Iron and Steel Institute. He pointed out that the metal can also has become more attractive in the last few years, with a drop in its price and and a reduction in its weight of up to 40 percent. But advances in plastic packaging do provide a challenge.

"Plastics are sexy," Wilson sighed. But steel can makers still have a few packaging tricks of their own up their sleeves. Can makers eventually may be able to eliminate ripples from metal cans, giving them a sleeker, more appealing surface. Also, by coating the cans in plastic and eliminating sharp angles, metal cans could be placed in a microwave, Wilson said.

Hercules Inc., a plastics producer in Wilmington, Del., projects large growth in barrier plastics. Alan Hinkle, director of quality assurance, tentatively predicts a market of up to a billion pounds, although the company currently only sells a fraction of that amount. "Any major food processor has -- in test -- barrier products," he said. The Society of the Plastic Industry Inc. also predicts a large growth of the barrier plastic products.

"Almost everything that's in other packaging now is apt to find itself into plastic eventually," said Jerome H. Heckman, SPI spokesman.

"You're getting away from cans as we know it," said Mike Caparon, director of marketing communications in the Dow Chemical Co. plastics division. He said that metal cans do poorly in competition with frozen food, and that an attractive package is the key to selling a product. Convenience is also important, he said, adding that food packages should be "properly designed and color-coordinated and ready to go."

One challenge Dow sees is making a plastic container that can be filled quickly enough on traditional food-processing lines. Production lines can fill 2,400 beer cans in a minute, which is a hard act for plastic to follow.

Thermoforming U.S.A., a Columbus, Ohio, company, is developing a plastic soft drink container for Coke's competitors that will keep the carbonation from leaking too quickly, according to sales engineer Gayle Davis. She said that the smaller bottles are tricky because, while larger PET soft drink bottles manage to keep the carbonation in, smaller bottles have a larger bottle-surface-to-volume ratio, causing the carbon dioxide fizz to leak out too quickly.

"The plastic can will go through the same evolution" as the metal can, she said. Davis claimed that the plastic can soon will fit into existing package lines and match the filling speed of the metal can.

While plastics and food manufacturers fret over perfecting the plastic can, environmentalists worry about recycling the man-made material. Neil Seldman, director of Waste Utilization for the Institute for Self Reliance, said that plastics manufacturers are only in the very early stages of attempting to recycle plastics. Some PET bottles are chopped up and reused, but he said that the industry must organize itself in the same way that glass and aluminum manufacturers have to recover material.

Kenton Osborn, manufacturing and technical manager in E. I. du Pont de Nemours & Co.'s packaging products division, said that plastic is more expensive than glass and metal now, but that a crossover point will occur in a few years and Du Pont has developed its own barrier resins in the ethylene vinyl alcohol group. Container manufacturers will be able to log significant savings in energy, he said. "The transition is the biggest problem in terms of time and money," Osborn said.