Fairfax County began enforcing its controversial soft-drink container ordinance yesterday, but a police check of 27 stores from Route 1 to McLean showed no violations of the new law.

Throughout the county, shoppers discovered that popular soft drinks like Coca-Cola, Pepsi-Cola or 7-up were generally available only in returnable bottles. At the big chain stores - like Giant, Safeway and A&P - shelves of soda in throwaway bottles and cans were shrouded with plastic and they were not available for sale.

Because throwaway bottles cannot be sold unless they are marked with a sticker saying "Washington Metropolitan area, five-cent refund," most stores did not offer them for sale. Store officials claimed that the job of placing stickers on the bottles was too laborious and time-consuming.

The ordinance, which soft-drink distributors unsuccessfully have sought to block with a court injunction, bans sofe-drink cans with disposable pop tops and requires merchants to pay a refund of at least five cents on each used container that is turned into them.

The ordinance, which covers only carbonated beverages, was passed in December, 1975, but its implementation was held up until Thursday to give bottlers, merchants and the public enough time to understand the law and adjust to it.

But even yesterday, the first day the law was enforced, there were isolated cases of confusion.

At the 7-Eleven store near Tysons Corner, for example, personnel had removed from the shelves all products in pop-top cans, even cheese dips and potato chips.

"That's what Southland (the company that owns 7-Elevens) said to do," a clerk said. "They said all pop-tops had to go."

"He misunderstood the order," said Charles R. Sweeney, merchandising manager of Southland's Springfield district office.

But there was misunderstanding in the Southland corporate offices, too. The company told its stores in Fairfax to remove all juices with pop-top cans, even though the ordinance covers only cans containing carbonated beverages.

Under the ordinance, shopper can buy uncarbonated soft-drinks - such as orangeade and chocolate drink - in pop-top cans or no-deposit throwaways, but distributors and store owners generally weren't offering these items yesterday because, some of them said, they wanted to be cautious.

In their bid for an injunction blocking the ordinance, which will be decided by the Senate Supreme Court Tuesday, soft-drink distributors have argued that the law is vague.

The purpose of the law is to help reduce roadside litter. A similar ordinance was passed in Montgomery County, Md., but won't take effect until Jan. 1.

Although opponents of the Fairfax ordinance predicted that it would create widespread confusion and hardship, not to mention shortages, a spot check of stores and their customers yesterday indicated that most problems were isolated.

There were ample supplies of popular soft drinks in returnable bottles at all stores that chose to stock them. There was not, however, a full range of sizes.

Most returnables were in the 16-ounce bottle, with some in smaller sizes. According to Jay F. Davis, executive vice president of the Washington 7-Up Bottling Co., local bottlers do not have machinery that can wash bottles that hold a quart or more, and therefore can't offer soda in returnables in those sizes, even though they are popular among consumers.

Davis said that if the ordinance survives its court test, "there will be a crunch, but a short one," in keeping store shelves and coolers filled with soda in returnable bottles. There is a possibility of a labor strike at the major glass-container companies, but a walkout, Davis said, would disrupt throwaway bottle as well as returnable supplies.

Some stores - the Peoples and Dart Drug chains, for example - chose to keep soft-drink shelves empty until the State Supreme Court reaches a decision on the Fairfax ordinance.

"We're selling a lot of beer instead," said Norma Bland, assistant manager of the Peoples in the Oakton Shopping Center.

At the nearby Giant, manager Crandall Graves said, "There have been no real problems . . . We've got 500 cases of returnables and we'll be getting 200 more.That should take care of our needs for the weekend. . . . Most people are taking it in stride."

Walking into the store with a carton of empty returnable beer bottles, Mike Turley, 25, said he supported the law wholeheartedly. "If you have nonreturnables," he said, "people just throw them out the window of the car. You bust your tires out on them. It's happened to me."

At a 7-Eleven on Maple Avenue in Vienna, 21-year-old Donna Holliday, made her exit swigging on a 16-ounce returnable RC Cola that cost her a nickle less than the 16-ounce throwaway that 7-Eleven is not selling for the time being. The returnable costs 30 cents (plus five cents refundable deposit), while the throwaways used to costs 35 cents.

Throughout the county, soda in returnable bottles was cheaper by the ounce than throwaways. At the Giant at Tysons Corner, the unit cost per quart for returnables (excluding deposit) ranged from 40 to 50 cents. The price range for throwaways - which wre not for sale was 52 to 56 cents.

Sweeney at 7-Eleven said returnable are a good deal for consumers - "if they don't mind returning the bottles" - but he said it will be a hardship for stores and distributors because they will have to find additional room for bottle storage.

Davis of 7-up said that if stores decide to sell throwaways - which, under the ordinance can be returned for a refund - we'd have to bust out walls" to make room for the bottles.

Occasionally, establishments that sell soft drinks found it necessary to improvise in order to obey the ordinance and yet serve customers.

In the Massey Building, where Fairfax officials drafted the law, the cafeteria customarily serves soft drinks in pop-top cans. But yesterday, to stay within the law, personnel opened a number of drinks, then poured them in coffee cups and wrote abbreviated labels ("Dr. P" for Dr. Pepper) on lids.

Deputy County Executive J. Hamilton Lambert, standing in the cafeteria line, said Fairfax County is obeying the ordinance, I'll have you know."