Astragalus leucolobus is endemic to California and at present there is some uncertainty about its precise distribution range, but on the basis of the literature data and the available specimens, the estimated extent of occurrence (EOO = 50,000 km²) does not meet the threshold for the species to be rated as threatened, based on criterion B. However, it has been estimated that the total number of mature individuals is less than 10,000. NatureServe (2009) estimated the total number of individuals comprised between 3,500 and 10,000) and a population decline of 10-50% has been observed in the last 10 years, due to the fact that the species is quite sensitive to disturbance (urbanization and the impact of off-the-road vehicles) and its distribution range is close to major populated places (e.g. Los Angeles), hence the species is rated as Vulnerable. The species needs to be monitored over a longer period of time to make sure of its status and dynamics and that it does not fall into a higher category in the near future.

Astragalus leucolobus is endemic to California (USA), where it occurs in the montane areas of San Bernardino, Los Angeles, Riverside, Ventura, Inyo and Kern counties (California Native Plant Society 2010, NatureServe 2009). A. leucolobus has also been reported from San Benito County, Anacapa Island (California) and Baja California (Mexico), but as these appear to be in areas of unsuitable habitat for this species (e.g. desert and low altitude) they have been excluded from the assessment.

The species has been recorded as being uncommon to occasional (White and Wood #61, Provance and Soza #895, White and Tennnant #6902, White and Hannon #9674) or abundant (Swinney #4746, White #11705, White #7456, Soza and Gross #1474) in its distribution range. The species' population size has been described as fairly small, as populations usually consist of up to 1,000 individuals (NatureServe 2009), the total number of individuals has been estimated to be between 3,500 to 10,000 (NatureServe 2009) and the population trends is considered to be declining (10-50% in the last 10 years or 3 generations).

A. leucolobus is a caespitose perennial herb which grows in montane coniferous forest, sagebrush scrub, alluvional shrubland, mixed evergreen forest, pebble plains, Pinyon-Juniper woodland and chaparral, riparian and meadow vegetation in some areas. NatureServe (2009) states that the species does not recover well from disturbance.

Threats to A. leucolobus are urbanization (development and tourist industry) and off-road-vehicles (CNPS 2001), as the species has been described as not able to recover well from disturbance (NatureServe 2009). Other threats include woodcutting, mining, vandalism, recreational activities and possibly burros (NatureServe 2009).

There are no known conservation measures specifically for A. leucolobus, but the species is currently known to occur in some protected areas, such as Bernardino National Forest, California Department of Fish and Game Baldwin Lake Preserve, Angeles National Forest and Los Padres National Forests. Samples of seed of A. leucolobus should be collected and stored as an ex situ conservation measure. The species has been assessed as Imperiled (G2) from NatureServe (2009), which is equivalent to IUCN category Vulnerable.