NEW YORK - The credit rating agency Standard & Poor's on Friday cut the United States' credit rating to AA+ from AAA, citing three fundamental reasons for the downgrade, the first ever in US history.

Debt burden worry

According to S&P's judgment, the debt situation of the United States doesn't satisfy the requirement of an AAA rating.

S&P compared US debt with the other four countries with AAA ratings: Canada, France, Germany and Britain.

It estimated the five countries will have net general government debt to GDP ratios this year ranging from 34 percent of Canada to 80 percent of Britain, with the US debt burden at 74 percent.

S&P predicted the net public debt to GDP ratios will range between 30 percent of Canada and 83 percent of France, with the US debt burden at 79 percent.

Although the US ratio of net public debt to the GDP was not the highest among the five countries, the rating agency projected that the net public debt burden of the other four countries will begin to decline, either before or by 2015.

Fiscal plan "not enough"

On August 2, US President Barack Obama signed legislation designed to reduce the fiscal deficit by $2.1 trillion over 10 years.

However, according to S&P's calculations, a good "down payment" on fixing the country's finances would be at least $4 trillion.

"The downgrade reflects our opinion that the fiscal consolidation plan that Congress and the administration recently agreed to falls short of what, in our view, would be necessary to stabilize the government's medium-term debt dynamics," S&P said.

The rating agency believed the prolonged controversy over raising the statutory debt ceiling and the related fiscal policy debate indicated that further near-term progress containing the growth in public spending, especially on entitlement, or on reaching an agreement on raising revenues is less likely than previously assumed and will remain a contentious and fitful process.

Lose faith on policy makers

S&P questioned US policy makers' eagerness to solve the debt problems by bipartisan efforts. Also, the rating agency blamed Democrats and Republicans for ignoring its earlier warnings.

On April 18, S&P assigned a negative outlook to US then-AAA rating, warning the debt ceiling should be raised to avoid a default. However, the action didn't draw much attention from policy makers who had decisive power to take quick measures.

The US debt would reach its ceiling of 14.3 trillion on August 2. If the debt ceiling was not raised, the United States would face an unprecedented default.

Through long, testy negotiations between the two parties in Congress, the plan was finally passed just before the August 2 deadline. However, patience and trust in US policy makers diminished as time went by.

"The effectiveness, stability, and predictability of American policymaking and political institutions have weakened at a time of ongoing fiscal and economic challenges to a degree more than we envisioned," S&P said.

Also, as the difficulties behind the debt problems still loom ahead, S&P worried that US policy makers could not react properly and effectively to the "government debt dynamics" any time soon, given their recent performance on dealing with the debt ceiling.