WASHINGTON - Goldman Sachs reaped "billions and billions of dollars" in profits by secretly betting in 2006 and 2007 that the U.S. housing market would crash, a strategy that conflicted with the interests of its clients who were still buying the firm's risky mortgage securities, Senate investigators said Monday.

"The evidence shows that Goldman repeatedly put its own interests and profits ahead of the interests of its clients," Sen. Carl Levin, D-Mich., chairman of the Permanent Investigations Subcommittee, told a news briefing. "I think they've been misleading to the country."

The panel provided a detailed glimpse of its findings from an 18-month investigation into the world's most prestigious investment bank, setting the stage for a hearing Tuesday at which Goldman's chief executive, Lloyd Blankfein, and six other company executives will give sworn testimony.

Blankfein plans to tell lawmakers that the day the Securities and Exchange Commission accused his firm of securities fraud was "one of the worst days" in his life.

According to his prepared testimony, released on Monday by Goldman, Blankfein plans to strike his most conciliatory tone yet, saying that he supports financial regulatory reform and arguing that his bank and others provide an important economic function, helping to manage money for pension funds and others and helping to distribute capital to companies.

The Senate committee released e-mail messages over the weekend in which Blankfein and other executives discussed the firm's bet against mortgages in 2007, just as the housing market began to fall apart.

In his prepared testimony, Blankfein insisted -- as the firm did over the weekend -- that Goldman was not significantly shorting the market.

"We didn't have a massive short against the housing market and we certainly did not bet against our clients," Blankfein plans to say. "Rather, we believe that we managed our risk as our shareholders and our regulators would expect."