This study develops practical models and methods for the assessment of safety and capacity rating of existing steel girder bridges based on the reliability methods. One of the main objectives of the study is to propose a practical but realistic limit state model for safety assessment and LRFR rating criteria, which explicitly incorporates the degree of deterioration and damage as well as actual condition of steel girder bridges in terms of the damage factor and the response ratio. The damage factor proposed in the paper is defined as the ratio of the current estimated stiffness to the intact base-line stiffness of a member. And the nominal ultimate strength of the steel girder is determined according to the AISC-LRFD specification. The failure mode approach(FMA) is used for approximate estimation of the system reliability of existing steel bridges. Based on the observation and the results of applications to existing steel girder bridges, it may be concluded that the proposed methods which explicityly account for the uncertainties and the effects of degree of deterioration or damage, provide more realistic and consistent safety-assessment and capacity rating of existing steel bridges.