Republican Senator Mark Kirk and Democrat Joe Manchin have been working on a bill which they described as a bid to find middle ground, given some conservatives want to close the export credit agency and many Democrats want to expand its activities.
The Senate bill may give supporters of Ex-Im, which provides support for US exporters and the buyers of US goods, leverage to push ahead with extending the bank's mandate, which has to be renewed before June 30 if it is to remain open.
Documents seen by Reuters show the bill would cut the bank's lending cap to $135 billion, from $140 billion currently, and boost the share of support going to small business to 25 per cent from 20 per cent.
It would also ban "discrimination" based on industry - wording a Democratic aide said would end restrictions put in place by the Obama administration limiting the bank's financing for coal-fired plants to buyers in only the world's poorest countries.
The treatment of coal is sensitive for Democrats, and could be a deal breaker for some members of the party. Manchin, who hails from the coal-producing state of West Virginia, argues the change will help preserve jobs in the struggling industry.
Ex-Im bills introduced in the House have support from more than half that chamber's lawmakers but have stalled amid staunch opposition from Ex-Im critic Jeb Hensarling, a Republican who chairs the committee responsible for the bank and is influential in determining which bills come up for a vote.
Critics charge that Ex-Im's support for overseas buyers of US goods, such as Boeing Co planes, gives foreign firms an edge over US competitors.
The Senate bill includes some reforms suggested in the House, including regular reviews of fraud controls and the appointment of a chief ethics officer.
Ex-Im spokesman Matthew Bevens said the legislation was in line with the bipartisan support the bank had enjoyed since its founding. "We look forward to working with all members of Congress to reauthorize Ex-Im Bank," he said.