The day after Standard & Poor’s took the unprecedented step of stripping the United States government of its top credit rating, the ratings agency offered a full-throated defense of its decision, calling the bitter stand-off between President Obama and Congress over raising the debt ceiling a “debacle.” It warned that further downgrades may lie ahead.

In an unusual Saturday conference call with reporters, senior S.& P. officials insisted the ratings firm hadn’t overstepped its bounds by focusing on the political paralysis in Washington as much as fiscal policy in determining the new rating. “The debacle over the debt ceiling continued until almost the midnight hour,” said John B. Chambers, chairman of S.& P.’s sovereign ratings committee.

Another S.& P. official, David Beers, added that “fiscal policy, like other government policy, is fundamentally a political process.”

Initial reactions from Congressional leaders suggested that S.& P.’s action was unlikely to force consensus on the fundamental divide over spending and taxes. Politicians on both sides used the decision to bolster their own long-standing positions.