Situation- and resource-aware security is essential for the process automation systems, composed of networked entities with sen- sors and actuators, that monitor and control the national critical in- frastructure. However, security cannot be addressed at a single layer because of the inherent dependencies and tradeoffs among crosscutting concerns. Techniques applied at one layer to improve security affect se- curity, timing, and power consumption at other layers. This paper argues for an integrated treatment of security across multiple layers of abstrac- tion (application, middleware, operating system including network stack, and hardware). An important step in realizing this integrated treatment of situation- and resource-aware security is first understanding the cross- layer interactions between security policies and then exploiting these interactions to design efficient adaptation strategies (i) to balance secu- rity, quality of service, and energy needs, and (ii) to maximize system availability. We propose a novel approach that employs a compositional method within an iterative tuning framework based on lightweight formal methods with dynamic adaptation.