WASHINGTON — The nation’s political leaders agreed on Sunday to spend and invest less money in the American economy, a step that economists said risks the reversal of a faltering recovery, in the hope of improving the nation’s long-term prosperity.

The emerging outlines of a deal to cut spending by at least $2.4 trillion over 10 years, with a multibillion-dollar down payment later this year, would complete an about-face in the federal government’s role from outsize spending in the immediate aftermath of the recession to outsize cuts in the future.

Last week brought the disconcerting news that the economy grew no faster than the population during the first six months of the year, in part because of spending cuts by state and local governments. Now the federal government is cutting, too.

“Unemployment will be higher than it would have been otherwise,” Mohamed El-Erian, chief executive of the bond investment firm Pimco, said Sunday on ABC. “Growth will be lower than it would be otherwise. And inequality will be worse than it would be otherwise.”