SAN FRANCISCO (MarketWatch) -- Fitch Ratings late Monday maintained its triple-A rating on the United States but lowered its outlook to negative from stable. "Fitch's current assessment is that the U.S. economic recovery will regain momentum in the latter half of next year and into 2013, and that a period of above trend growth will be subsequently followed by growth of at least 2 and 1/4% over the long term," the ratings agency said in a statement. Fitch, however, attributed the negative outlook to declining confidence that the country will be able to adopt timely fiscal measures to secure the rating following the failure of a so-called congressional supercommittee to trim $1.2 trillion from the federal budget over the next 10 year