Fairfax county began enforcing its controversial beverage container ordinance at midnight after a three-judge Virginia Supreme Court panel in Richmond postponed a ruling on a request by soft drink dealers temporily to block the law.

County officials had announced Wednesday they would not enforce the law, which became effective yesterday, until the Supreme Court acted. But the justices, after an hour-long hearing, said they wanted to review the case and would not render a decision on the law's legality until Tuesday.

The county said it decided to begin enforcing the law because a Fairfax Circuit Court judge earlier this week upheld the ordinance and because it had expected the Supreme Court to act yesterday.

"IT seems the bottlers have had their days in court," said county spokeswoman Jane Stern.

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The law bans the sale of carbonated, nonalcoholic drinks in cans with a detachable pop top and requires the placement of a sticker with the words"Washington Metropolitan Area. Five-cent return on the other soft drink containers. The sale of alcoholic beverages is not covered by the ordinance.

The idea behind the law is that with a refund value placed on the bottles and cans. Consumers will return the containers to merchants to get the money, rather than pitching the containers along highways or in parks.

The county, in an informal survey of dozen stores, determined that these large grocery chain stores had plenty of soft drinks in returnable containers available. Ranging from 16 cartons at one Safeway store in Springfield to 356 cartons at a Giant Food store also in Springfield. Stern said.

The county also said "a substantial number" of the stores were complying with the law yesterday. Even though it was not being enforced.

An informal survey of stores in the county by The Post showed that A & P. high's and Dart Drug stores were selling soft drinks in nonreturnable contaainers as usual while Safeway, Giant and 7-Eleven food stores were selling only drinds in returnable bootles and cans.

The request for temporary injunction against the law was sought last week by sex soft drink distributors and Charles Tabler, owner of Foodarama Supermarket in McLean. They contend the law is vague, irrational and burdensome.

Fairfax Circuit Court Judge James SKeith denied the request and ruled Monday that the law passed in December, 1975, is constitutional. Keith said the bottlers had 20 months to challenge the ordinance and waited until the last minute to "play fast and loose" with the courts.

Regardless of the three-judge panels decision on the temporary injunction Tuesday. The dealers still have a case in Fairfax Circit Court seeking to have the law thrown out permanently. Keith, in his three-page decision Monday said the dealers probably will not succeed in their eventual efforts to overturn the law.

Supreme Court Justices Harry L. Carrico, Richard H. Poff and A. Christian Compton deliberated for about 10 minutes yesterday after hearing arguments on the law. "We want time to study the file" on the case, Carrico said. "We'll try to let you have an answer by Tuesday. Monday's a holiday."

J.Sloane Kuykendall, the lawyer representing the soft drink distributors and Foodarama, argued that the ordinance will put some distributors sell soft drinks in disposable containers.

For more than half an hour Kuykendall contended that the wording of the orkinance is vague and that the definitions of beverage and beverage container are nto clear.

The beverages covered under the ordinance include "mineral water, soda water and other similar carbonated beverages..."

"We contend that 'similar carbonated soft drinks' is vague." Kuykendall said. "What are similar carbonated soft drinks? Who will know if they come in the purview of this ordinance?"

Kuykendall also said the ordinance defines a beverage container as being filled and sealed, but there is no definition for an empty beverage container.

"That may sound like nitpicking, but it is not," Kuykendall said. "A dealer doesn'thave to accept an empty bottle because it isn't defined in the law."

William Arnold, arguing for the county,said that the definitions are plain enough for the average person to understand and therefore the ordinance is not unconstitutionally vague.

"I think anybody of normal intelligence can tell" whether a beverage is carbonated or what an empty container is, Arnold said.

"If a temporary injunction is issued what harm could there be (for the county)in temporarily delaying enforcement. Until the case could be litigrated on its merits? Compton asked.

Arnold said consumers could be injured by swallowing the detachable metal pull tabs.

That's only after they've been dropped in the can," Comptonsaid, smiling.

Arnold added that county residents would have to pay for more litter clean-ups. Compton then asked how long would it take before the case could be heard in ciruit court. Arnold said he did not know.