WITH PREDICTABLE CRIES of gloom and doom, the throwaway-bottle-and-can lobbyists have all but snapped their caps battling over a Fairfax County ordinance - scheduled to take effect today - that would require a deposit of at least a nickel on soft-drink and mineral-water containers. To hear them tell it, Fairfax shoppers are in for The Big Parch, with nary a soft drink on the shelves of their county. And that's not all; as supplies dry up in Fairfax, you must brace yourself for an outbreak of bootleggeing as thirsty citizens sneak over the borders in search of treasured throwaways.

We trust that the smart shoppers in Fairfax can see through all this supercharged carbonation. For one thing, they must have discovered by now that, where returnable bottles are readily available, the savings can be considerable. After all, you're really borrowing the bottle. As for the question of whether the soft-drink people are actually capable of providing their products in returnable bottles, well, we take you now back to the pages of this newspaper - and others - of two years ago. There you will find ads by the local Coca-Cola bottling company specifically extolling the returnable bottle and stressing the savings they offer.

Those ads rightly pointed out that, by buying the product in a reusable bottle, the customer is paying only for the drink and not for the bottle each time. "The beauty of recycling" with the deposit bottle, the ads noted, is that "it recycles itself." To encourage greater sales in returnables, the ad campaign urged radio listeners to apply pressure on stores that didn't carry them. The Coca-Cola bottlers are among those expected to be in court today fighting for the Farifax ordinance, and it will be exceedingly interesting to see exactly how they reconcile today's opposition with their support for the idea two years ago.

One point the retailers are making is that it really isn't convenient for them to make the switch this week. But it isn't as if they were told overnight to overhaul their stock. The Fairfax County Board of Supervisors passed the ordinance in December 1975. Besides, the stores can still sell the throwaways, but with a deposit.

None of this is say that all is certain to go smoothly. Fairfax is one of the pioneer jurisdictions in this sensible shift away from the cost, waste, mess and danger of accidents that accompany the use of throwaway glass metal for bottling, and there are bound to be some transitional difficulties. But Montgomery County, too, has a good law set to take effect in January. For all the inevitable inconveniences that may be encountered in the early days, this is a healthy trend. We hope that sensitive legislators in other jurisdictions hereabouts will move vigorously to enact the same legislation.