New York, April 19 (IANS/EFE) Standard & Poor's Ratings Services announced Monday that it downgraded the long-term outlook for US sovereign debt from stable to negative.

At the same time, S&P continues to give Washington's long-term and short-term debt the highest ratings, AAA and A-1+, respectively.

"Our negative outlook on our rating on the US sovereign signals that we believe there is at least a one-in-three likelihood that we could lower our long-term rating on the US within two years," S&P credit analyst Nikola G. Swann said in a statement.

The US remains a "high-income, highly diversified, and flexible economy" with "a strong track record of prudent and credible monetary policy".

"Although we believe these strengths currently outweigh what we consider to be the US's meaningful economic and fiscal risks and large external debtor position, we now believe that they might not fully offset the credit risks over the next two years at the 'AAA' level," Swann said.

He cited what he called "a significant risk that Congressional negotiations could result in no agreement on a medium-term fiscal strategy until after the fall 2012 Congressional and presidential elections".

"More than two years after the beginning of the recent crisis, US policymakers have still not agreed on how to reverse recent fiscal deterioration or address longer-term fiscal pressures," Swann said.

Under S&P's "optimistic scenario", which posits average annual growth of nearly 4 percent, the US "fiscal profile would be less robust than those of other AAA rated sovereigns by 2013", the analyst said.