WE HAVE A HUNCH, based on nothing more than an unscientific spot survey of nieghborhood markets here and there, that more and more beverage manufacturers, bottles and distributors are supplying area stores with drinks in returnable containers. It's not that the lobby to promote the proliferation of throwaway bottles and cans has given up; that well-financed campaign continues in advertisements and in the courts.But now that Fairfax County has some sensible controls on throwaways in effect - and with laws now scheduled to take effect in Montgomery County and Loudoun County in a matter of months - perhaps the smarter industry phanners will see a chance to take the lead and capture a good slice of the consumer market by stepping up their sales in returnables.

Careful shoppers, certainly, are discovering that where stores are well stocked with returnables (or with the throwaways covered by the Fairfax deposit law), selectivity and savings can go hand-in-hand. So the more jurisdictions that make the switch in this region, the simpler shopping will be.

Though Fairfax County became the first area jurisdiction in which a law went into effect, the movement in Loudoun goes back before 1971, when the county supervisors approved a law that was challenged by the beverage industry and found unconstitutionally vague. The latest Loudoun law, passed unanimously on Monday, not only addresses deficiencies in the earlier legislation, but moreover goes further than the law in effect in Fairfax. In addition to containers of carbonated soft drinks, it includes beer containers (as does the Montgomery County law recently upheld by the Maryland Court of Appeals).

Previous attempts by Loudoun to include beer containers have been knocked down in Virginia ongrounds that alcoholic beverages are the exclusive domain of the state Alcoholic Beverage Control Board. So the supervisors say their new law seeks to regulate litter, not the beer in the containers. We hope this interpretation of local option in Virginia is upheld.In any event, drafters of the Loudoun ordinance wisely included a clause stating that if any part of the law is found unconstitutional or invalid the remaining portions will not be affected.

After a six-year effort by the county's elected officials to start controls on throwaways, the Loundoun action may turn out to have a constructive effect on Virginia jurisdictions beyond the metropolitan area. Copies of the Loudoun ordinance have been sent to local officials throughout the state; and on Monday, board members from Caroline County were on hand to praise Loudoun supervisors for passing the bill. Until enough sensitive members of Congress recognize the importance of enacting federal standards to phase out the costly waste and senseless consumption of energy and natural resources that have been connected with throwaways, consumers will have to look to their state and local leaders for relief.