You can assign permissions to users and groups on the following web service objects:
Web service operation
When you assign permissions on a web service object, the user or group inherits the same permissions on all objects that belong to the web service object. For example, you assign a user execute permission on a web service. The user inherits execute permission on web service operations in the web service.
You can deny permissions to users and groups on a web service operation. When you deny permissions, you configure exceptions to the permissions that users and groups might already have. For example, a user has execute permissions on a web service which has three operations. You can deny a user from running one web service operation that belongs to the web service.