George W. Koch, who was shunned by many fellow members of the swank Congressional Country Club at Potomac because he fought to assure full pay for the club's service employes, has won a five-year court battle to inspect the club's books in furtherance of his crusade.

Koch, a political conservative who is president of the Grocery Manufacturers Association of America, began his effort in the mid-1970s after some club employes complained to him that the club was routinely skimming 20 percent of their pay.

The Maryland Court of Special Appeals ordered a second trial in the case last April, overturning Montgomery Circuit Judge John J. Mitchell's decision to dismiss the case on his finding that Koch had a vendetta against the club and a habit of trying the case in the news media.

Earlier this month, however, the club agreed in a consent judgment before the appellate court to permit Koch to see its financial records under conditions that protect the privacy of both club members and employes.

As far back as 1948, the club began a practice of deducting 20 percent of the pay of such service employes as waiters and cooks, ostensibly to create a pool of money to equalize the earnings of employes who earn tips and those who don't. The Maryland attorney general's office ruled that such a practice is legal if the affected employes agree to it. Although Congressional employes had not so agreed, the statute of limitations had run out and no prosecution was possible.

" . . . I'm grateful," said Koch. " . . . By pressing this case, despite the club board and management's opposition, I've been able to assure the righting of past mistreatment of club employes and to assure that employes will be treated honestly and fairly in the future."