A shutdown of the U.S. government would reduce fourth-quarter economic growth by as much as 1.4 percentage points depending on its length, economists say, as government workers from park rangers to telephone receptionists are furloughed.

Mark Zandi of Moody's Analytics Inc. estimates a three-to-four week shutdown would cut growth by 1.4 points. Moody's projects a 3 percent rate of growth in the fourth quarter without a closure. A two-week shutdown starting Oct. 1 could cut growth by 0.3 percentage point to an annualized 2.3 percent rate, according to St. Louis-based Macroeconomic Advisers LLC.

A shutdown would slow the expansion because output lost when workers are furloughed subtracts from gross domestic product. The combined prospect of a budget standoff between the White House and Congress and haggling over the debt ceiling could have a bigger impact on the economy as businesses hold off on investment and households delay spending.