WASHINGTON – A panel investigating the roots of the financial crisis will press current and former executives of Citigroup Inc. at hearings this week about the bank’s role in spreading trillions of dollars in risky mortgage debt through the banking system.

The hearings are the first by the Financial Crisis Inquiry Commission to focus on a single company. Witnesses include former Citi CEO Chuck Prince and former Chairman Robert Rubin.

The panel also will hear from former Federal Reserve Chairman Alan Greenspan; a former risk officer with failed subprime lender New Century Financial Corp.; and former executives and regulators from government-backed mortgage giant Fannie Mae. The three days of testimony are designed to provide a firsthand accounting of decisions that inflated a mortgage bubble and triggered the financial crisis.

Much of the tension at hearings Wednesday and Thursday will come as the 10 bipartisan commissioners examine Citi’s role in financing, packaging and selling risky mortgage loans.

Citi was a major subprime lender through its subsidiary CitiFinancial. The bank pooled those loans and loans purchased from other mortgage companies and sold the income streams to investors. As borrowers defaulted, Citi absorbed losses on mortgage-related investments it held on and off its books.

Mortgage troubles at Citi, defunct investment bank Bear Stearns and elsewhere exposed cracks in the financial system. In late 2007 and throughout 2008, those fissures grew into a full-fledged credit crisis that crippled the global economy.

Congress created the FCIC last year to examine the causes of that crisis. It is structured like the 9/11 panel that examined intelligence failures preceding the terrorist attacks of Sept. 11, 2001.

Like that panel, the commission has authority to issue subpoenas to compel witnesses to testify or force companies to turn over documents. The commission is charged with examining 22 topics — from executive compensation to tax policy — in a report it must issue Dec. 15.

Greenspan’s testimony Wednesday will open the hearings. Critics say his policy at the Fed of keeping interest rates low encouraged lending to borrowers who had little or no chance of repaying.

Wednesday’s remaining two panels will include testimony on subprime lending and risk management at Citigroup. Former risk management executives are expected to say they sounded alarms about the growing danger of Citi’s mortgage lending and finance activities but were ignored by senior management.