WASHINGTON — Congressional leaders dug in their heels on Tuesday against any quick deal to resolve a looming fiscal disaster before the election, even as a major ratings agency warned that it would downgrade the government’s debt if no solution was found by year’s end.

Democratic leaders have warned their own members to tone down any discussion of a short-term resolution to the “fiscal cliff,” betting that Republican fears over the January deadline will drive them to the negotiating table shortly after the November election.

Speaker John A. Boehner, reacting to the downgrade notice from Moody’s Investor Service, said it underscored the Republican position that the nation’s precarious fiscal condition could be addressed only by cutting government spending.

“The threat to American jobs comes not from action on our debt, but from inaction on our debt,” he said. “The president and his economic advisers have consistently perpetuated the myth that downgrades are caused by efforts to force the government to stop spending money we don’t have.”

The Moody’s warning comes a year after its rival, Standard & Poor’s, downgraded the United States’ credit worthiness after the protracted stalemate over raising the nation’s statutory borrowing limit.

Like S&P, Moody’s emphasized political dysfunction more than soaring government debt. The agency said Washington must come to agreement to head off billions of dollars in simultaneous tax increases and spending cuts scheduled to begin in January — and to put the government on a sustainable fiscal trajectory. Only then would the United States keep its AAA rating.