WASHINGTON — Lawmakers returning to Washington from their summer recess are plunging immediately into bitter, partisan debate over the Iran nuclear accord.

The deal struck by Iran, the U.S. and five world powers in July is aimed at curbing Iran’s nuclear program in exchange for hundreds of billions of dollars in relief from economic sanctions.

Republicans who control the House and Senate strongly oppose the pact, saying it makes dangerous concessions to Iran. They hope to push through a resolution of disapproval this week.

If they succeed, President Barack Obama would veto the resolution, and Democrats have already lined up enough votes to uphold his veto.

The question as Congress reconvenes today from a five-week break is whether the disapproval resolution will get through the Senate — or whether Democrats will have the votes to block it with a filibuster.