WASHINGTON — Social Security is so overwhelmed by disability claims that some officials are awarding benefits without adequately reviewing applications, potentially adding to the program's financial problems as it edges closer to the brink of insolvency, congressional investigators say in a new report.

In more than a quarter of the 300 cases reviewed by congressional staff, decisions to award benefits "failed to properly address insufficient, contradictory or incomplete evidence." In many cases, officials approved disability benefits without citing adequate medical evidence or without explaining the medical basis for the decision, according to the report by the Republican staff of the Senate Permanent Subcommittee on Investigations.

In some cases, it appeared that administrative law judges struggling to reduce backlogs didn't take the time to review all the evidence, the report said. The judges are expected to rule on at least 500 cases a year, with one judge deciding an average of 1,800 cases a year for three straight years, the report said.