California has been among the states hurt the most by the mortgage crisis. Because its laws, like those of 29 other states, do not require a judge to oversee foreclosures, the conduct of banks in the process is rarely scrutinized. Mr. Ting said his report was the first rigorous analysis of foreclosure improprieties in California and that it cast doubt on the validity of almost every foreclosure it examined.

“Clearly, we need to set up a process where lenders are following every part of the law,” Mr. Ting said in the interview. “It is very apparent that the system is broken from many different vantage points.”

The report, which was compiled by Aequitas Compliance Solutions, a mortgage regulatory compliance firm, did not identify specific banks involved in the irregularities. But among the legal violations uncovered in the analysis were cases where the loan servicer did not provide borrowers with a notice of default before beginning the eviction process; 8 percent of the audited foreclosures had that basic defect.

In a significant number of cases — 85 percent — documents recording the transfer of a defaulted property to a new trustee were not filed properly or on time, the report found. And in 45 percent of the foreclosures, properties were sold at auction to entities improperly claiming to be the beneficiary of the deeds of trust. In other words, the report said, “a ‘stranger’ to the deed of trust,” gained ownership of the property; as a result, the sale may be invalid, it said.

In 6 percent of cases, the same deed of trust to a property was assigned to two or more different entities, raising questions about which of them actually had the right to foreclose. Many of the foreclosures that were scrutinized showed gaps in the chain of title, the report said, indicating that written transfers from the original owner to the entity currently claiming to own the deed of trust have disappeared.

Banks involved in buying and selling foreclosed properties appear to be aware of potential problems if gaps in the chain of title cloud a subsequent buyer’s ownership of the home. Lou Pizante, a partner at Aequitas who worked on the audit, pointed to documents that banks now require buyers to sign holding the institution harmless if questions arise about the validity of the foreclosure sale.