Large Language Model (LLM) agents are increasingly expected to interact with external environments rather than only generate text. A key challenge in this process is to accurately and efficiently ground high-level agent intents into valid executable action sequences, especially when the environment consists of multiple interacting modules. To address this challenge, we introduce executable action programs (EAPs), a restricted Python-based intermediate representation between textual agent intents and structured environment-module action calls, which leverages the expressive power of Python to explicitly represent complex behavioral sequences, their branching relationships, and cross-module data dependencies. Based on this representation, we implement EAPRouter, which generates, validates, executes, and reuses EAPs through an agent-EAP interface and a lightweight environment module integration protocol. We evaluate EAPRouter on real agent-environment interaction traces from social simulation, a demanding application scenario with multi-agent, multi-module, and repeated interaction patterns. Experiments show that EAPRouter achieves a 60.0% grounding success rate with Kimi-K2-Instruct, outperforming the SOTA function-calling baseline by 31.6%. It also improves over the strongest baselines by 11.5%-25.4% on GLM-4.7, Claude Opus 4.5, and Gemini 2.5 Flash, with smaller gains on less code-capable models. On the cross-domain NESTFUL v2 benchmark, EAPRouter matches ReAct’s executable accuracy (83.8% vs. 84.9%) while reducing LLM calls, tokens, and execution time by about 80%. EAP pre-generation further handles over 70% of interaction requests, cache reuse covers 66.5% of the remaining ones, and safety validation blocks all tested unsafe payloads and prompt-injection attempts. The code is available at https://github.com/tsinghua-fib-lab/EAPRouter.