David Walker, comptroller general of the US, issued the unusually downbeat assessment of his countryâ€™s future in a report that lays out what he called â€œchilling long-term simulationsâ€.
These include â€œdramaticâ€ tax rises, slashed government services and the large-scale dumping by foreign governments of holdings of US debt.
Drawing parallels with the end of the Roman empire, Mr Walker warned there were â€œstriking similaritiesâ€ between Americaâ€™s current situation and the factors that brought down Rome, including â€œdeclining moral values and political civility at home, an over-confident and over-extended military in foreign lands and fiscal irresponsibility by the central governmentâ€.
â€œSound familiar?â€ Mr Walker said. â€œIn my view, itâ€™s time to learn from history and take steps to ensure the American Republic is the first to stand the test of time.â€
â€œIâ€™m trying to sound an alarm and issue a wake-up call,â€ he said. â€œAs comptroller general Iâ€™ve got an ability to look longer-range and take on issues that others may be hesitant, and in many cases may not be in a position, to take on.
â€œOne of the concerns is obviously we are a great country but we face major sustainability challenges that we are not taking seriously enough,â€ said Mr Walker, who was appointed during the Clinton administration to the post, which carries a 15-year term.
The fiscal imbalance meant the US was â€œon a path toward an explosion of debtâ€.
â€œWith the looming retirement of baby boomers, spiralling healthcare costs, plummeting savings rates and increasing reliance on foreign lenders, we face unprecedented fiscal risks,â€ said Mr Walker, a former senior executive at PwC auditing firm.
Current US policy on education, energy, the environment, immigration and Iraq also was on an â€œunsustainable pathâ€.
â€œOur very prosperity is placing greater demands on our physical infrastructure. Billions of dollars will be needed to modernise everything from highways and airports to water and sewage systems. The recent bridge collapse in Minneapolis was a sobering wake-up call.â€
Mr Walker said he would offer to brief the would-be presidential candidates next spring.
â€œThey need to make fiscal responsibility and inter-generational equity one of their top priorities. If they do, I think we have a chance to turn this around but if they donâ€™t, I think the risk of a serious crisis rises considerablyâ€.