AT this year's Frankfurt international auto show - the world's largest - the cars that can't yet be bought have nearly outshined the ones that can.For example, upstairs and away from the usual displays of Autobahn-blasting horsepower by Bayerische Motoren Werke AG (BMW) sits the "E1," one of this week's big attractions. Characterized by one German magazine as "a rolling egg," the E1 is not for sale. The small car is a "design study." Pull down on its distinctive BMW grill and out pops an electric cord. Making use of new sodium-sulfur battery technology, BMW is aiming to produce a zero-emission vehicle. Actual production of a BMW electric car is still years away. Nonetheless, company executives said it was important to display an electric car at this year's auto show. "We wanted to show what a zero-emission vehicle would look like," says Dr. Klaus Faust, managing director of BMW Technik, the BMW subsidiary responsible for making the E1, "and if you really want to make a zero-emission vehicle it has to be electric." Displays of futuristic experimental cars have always been an attraction at auto shows. This year, however, the topic has been pushed beyond mere theorizing by the presence here of numerous functioning prototypes of electric and alternative vehicles. What gives these vehicles more significance is the recent enactment in California of a regulation requiring manufacturers to sell zero-emission vehicles in that state by 1998. Virtually all the major car companies at this year's exhibition are presenting mockups of either electric or hybrid vehicles. Hybrids are cars which operate electrically but which can switch over to a small internal combustion engine to extend their range or increase speed. In a corner, well behind an elaborate stage show of leggy dancers and dazzling spotlights playing up Volkswagen's newest incarnation of its popular "Golf," there stands a tiny little car named "Chico." Barely 10 feet long and with its rounded plastic body painted mint green, "Chico" looks like a rolling version of Kermit the frog. Just right for hops around town perhaps. A Volkswagen brochure describes the three-doored four-seater as a design study for a hybrid electric/diesel powered city car. Volkswagen and the Swatch watch company, SMH in Switzerland, have formed a joint venture to produce a fashionable, recyclable, ecologically friendly urban vehicle. Could "Chico" be a sneak preview of the future "Swatch-Car"? Right now Volkswagen officials will only smile coyly and shrug. Car companies were eager to show environmental responsibility in other ways, too. All the major manufacturers produced exhibits displaying evidence of their recycling prowess. Earlier this year BMW opened a pilot version of a car disassembly plant. The company's announced goal is to produce a completely recyclable BMW. Plastics, used in increasing proportions on all cars, are now being coded to assist in identifying and sorting different types of plastics during the disassembly process. In an attempt to maintain attention on what was supposed to be the star of this year's show - its new "Golf III Volkswagen announced that the company will take back for recycling all of its new cars at the end of their working lives free of charge. GM/Opel has made the same offer for its new "Astra." And both companies are contemplating extending the programs to include earlier makes of their cars. In his opening address at this year's show, German Economics Minister Jugen Mollemann described the car industry as the "motor" of the country's economy. Every sixth job is directly or indirectly dependent on the automotive industry. Vehicle sales and exports make up a large proportion of the country's gross national product. So Germans are understandably cautious when a major overhaul of a vital industry is discussed. Concerns about the industry's future were voiced at a panel discussion entitled "People-Autos-Environment." Auto executives worried that the public's expectations of ecologically friendly vehicles are being raised beyond what their industry could realistically provide. A few even questioned whether it was a good idea to display cars like the Chico and E1. "Some politicians may be relying on electric vehicles too much," said Volkswagen's head of research and development Ulrich Seiffert, who pointed out that commercial production of electric and hybrid cars may be four to five years away. And even then they won't provide an inexpensive solution for city smog. "Small cars do not equate to small prices," says Prof. Seiffert, "an electric car would cost 70,000 deutsche mark right now." The Frankfurt International Auto Show continues until Sept. 22 at the Frankfurt exhibition grounds.