WASHINGTON  —  Alan Greenspan (search), who has dealt boldly with economic risks as chairman of the Federal Reserve (search) over the last 18 years, plays it safe when it comes to his own investments.

The Fed chief keeps all of his holdings in money market accounts and Treasury securities, which are considered the world's safest investment, a financial disclosure form for Greenspan, released Thursday by the central bank, shows. The Fed chief avoids any appearance of conflict that might be raised by stock holdings in individual companies.

Among his investment holdings in 2004 were three Oppenheimer IRAs in U.S. Treasury bills (search), each valued at $500,001 to $1 million.

Greenspan, who is 79 and expected to retire from the central bank next year, has urged Congress to deal with the looming financial crisis of the Depression-era Social Security (search) retirement system. The system faces massive strains as a wave of baby boomers begin retiring in 2008. The Fed chief also has called on upcoming retirees to make sure they have their own financial houses in order.