Credit rating agency Standard & Poor's says it will not downgrade the U.S. government's credit rating because a Congressional committee failed to come up with a plan to trim deficits by at least $1.2 trillion over the next decade.

S&P in August cut its rating of long-term U.S. Treasury securities by one notch from AAA to AA+, the first such downgrade of U.S. government debt in history.

In a brief statement Monday, S&P said it did not plan a further downgrade of the rating based on the supercommittee's failure to agree on a plan. But S&P warned that its present rating is based on the expectation that automatic cuts will take effect in January 2013. Some Republicans are vowing to block the defense spending cuts.