In the modern context of global changes, the study of the influence of administrative and legal factors on the sustainable development of regions is of particular relevance, which is also due to the hyperdynamics of the external environment. The main purpose of the article is to identify and streamline the main administrative and legal factors influencing the formation of sustainable development of the region in a changing external environment. Key research methods are the method of hierarchical analysis, paired comparison, expert analysis and the Delphi method. A scientific question has been formulated based on the results of a literature review, which is how to more effectively implement administrative and legal support for the formation of sustainable development of the region. Valid methods are disclosed due to their step-by-step application. An analysis of the dynamics of key indicators of sustainable development of one of the regions was carried out. A modern model for the formation of sustainable development of the region is proposed, considering the conditions of the changing external environment and focusing on administrative and legal principles, which is characterized by blocks and a schematic explanation. A methodological approach to modelling the definition and ordering of the main administrative and legal factors influencing the formation of sustainable development of the egion in a changing external environment has been developed. Based on the results of the modelling, it was determined that the most significant factors of influence within the framework of administrative and legal support for the formation of sustainable development of the Lviv region in a changing external environment are martial law, administrative court proceeding and local self-government and decentralization. The effectiveness of the proposed method has been proven through the ability to satisfy all information needs of subjects of sustainable development in the region. The practical significance of the research results is revealed in the possibility of using the proposed model and methodological approach in the work of public services and the public administration system of the region