The New York attorney general has requested information and documents in recent weeks from three major Wall Street banks about their mortgage securities operations during the credit boom, indicating the existence of a new investigation into practices that contributed to billions in mortgage losses.

Officials in Eric T. Schneiderman’s office have also requested meetings with representatives from Bank of America, Goldman Sachs and Morgan Stanley, according to people briefed on the matter who were not authorized to speak publicly. The inquiry appears to be quite broad, with the attorney general’s requests for information covering many aspects of the banks’ loan pooling operations. They bundled thousands of home loans into securities that were then sold to investors such as pension funds, mutual funds and insurance companies.

It is unclear which parts of the byzantine securitization process Mr. Schneiderman is focusing on. His spokesman said the attorney general would not comment on the investigation, which is in its early stages.

Several civil suits have been filed by federal and state regulators since the financial crisis erupted in 2008, some of which have generated settlements and fines, most prominently a $550 million deal between Goldman Sachs and the Securities and Exchange Commission.