Given the global trends towards an increase in the number and complexity of cyberattacks, there is an urgent need to ensure the resilience of information technology systems (ITS), especially sectoral systems that play a critical role in public functioning, socio-economic development and national security. In this regard, at the level of the state, the solution of the problem of ensuring the security of critical infrastructure becomes a priority in the process of reforming the defense and security sector of the Republic of Kazakhstan. In this context, there is an urgent need to develop methods and models for attributing IS to critical infrastructure objects in order to ensure national security of Kazakhstan. This study presents a model for calculating the quantitative criterion of information systems sustainability based on the method of hierarchy analysis. This approach allows us to obtain quantitative indicators of IS sustainability by processing expert evaluations. The application of this model simplifies the procedure of expert selection, avoids the complexities of expert data processing and provides IS assessment with limited statistical data. The developed model allows us to move from a qualitative assessment, represented by an ordered series of alphanumeric combinations reflecting the levels of realized services, to a quantitative assessment in the form of a ratio of functional profiles of security.