After a closed-door meeting of Democratic senators, Sen. Dianne Feinstein, D-Calif., urged her colleagues to postpone action until the fall, when a better economic climate might help.
But some lawmakers say a delay would push the issue closer to the Nov. 2 elections, in which Republicans hope for major House and Senate gains, making passage even less likely.
Only a handful of GOP senators have said they might back a plan to set prices on heat-trapping carbon emissions. A compromise plan to put controls on emissions from only utilities has not attracted the 60 votes needed to advance it in the 100-member chamber.
Senate Majority Leader Harry Reid said Democrats will meet Thursday to seek "a way forward." Several colleagues said he faces an uphill hike.
The House voted 217-205 last year for a "cap and trade" energy plan. It would create economic incentives to limit heat-trapping gases from power plants, vehicles and other sources.
The issue quickly bogged down in the Senate. Now, with time running short, even a sharply scaled-back version is in trouble.
Congress traditionally takes a long August recess. After Labor Day, the fast-approaching election will make difficult issues all the harder to resolve.
"Republicans are basically slow-walking us out of time," Sen. Debbie Stabenow, D-Mich., said Tuesday.
Some senators want a bill that deals only with non-carbon issues such as greater energy efficiency and cleaning up the Gulf oil spill. Others say such a narrowly focused bill would be a waste of time and opportunity.
Sen. Joe Lieberman, a Connecticut independent who works with Democrats on energy, said Democrats are "of many minds on this." Most members, he said, want "a strong energy-independence, emission-reduction, job-creation bill."
"We know that this is difficult in an election year, but I think the public wants us to take a strong action on energy," Lieberman said.
Lieberman and Sen. John Kerry, D-Mass., the bill's leading sponsors, met Tuesday with the Edison Electric Institute, the trade group that represents about 70 percent of the U.S. electric power industry. No agreement was reached.
"The clock is our biggest enemy," Kerry said. "We have to figure out what is doable in this short span of time."