WASHINGTON — Come January, if Congress fails to act, spending cuts and tax increases large enough to throw the country back into recession will hit.

It is known in Washington as the “fiscal cliff.” But policy and economic analysts projecting its complicated and wide-ranging potential impact said the term “fiscal hill” or “fiscal slope” might be more apt: the effect would be powerful but gradual, and in some cases, reversible.

“The slope would likely be relatively modest at first,” Chad Stone, the chief economist at the Center on Budget and Policy Priorities, a research group based in Washington, wrote in a recent analysis. “A relatively brief implementation of the tax and spending changes required by current law should cause little short-term damage to the economy as a whole.”

The annual effect of the automatic tax increases and spending cuts would be enormous. The Congressional Budget Office has estimated that the budget deficit would shrink by more than half a trillion dollars from fiscal years 2012 to 2013 and that the economy would very likely enter another recession.