WASHINGTON -- Congress returns Tuesday to a crowded agenda of unfinished business overshadowed by the urgent need for President Barack Obama and lawmakers to avert the economic double hit of tax increases and automatic spending cuts.

One week after the elections, Republicans and Democrats face a daunting task in a lame-duck session that Capitol Hill fears could last until the final hours of Dec. 31. But even before serious budget negotiations can begin, lawmakers will tackle leftover legislation on trade with Russia, military budgets and aiding farmers still reeling from the summer's drought.

The first days back will be a mix of old and new - choosing down-ballot leaders in the Senate while new members get a crash course on how Congress operates.

Congress last met seven weeks ago.