WASHINGTON — Democratic leaders in the Senate plan to push a bipartisan energy proposal that would allow expansion of offshore drilling when Congress returns next week from a five-week recess.

The plan that would allow Virginia, Georgia, North Carolina and South Carolina to opt into leasing programs starting 50 miles off their shores now has the support of 16 senators — eight Democrats and eight Republicans.

However, it is expected to face opposition from lawmakers in both parties, and with Congress planning to meet for only three weeks before recessing again for the November election, its prospects are dim.

The proposal, not yet introduced as legislation, would also lift a ban on drilling off the Gulf coast of Florida, invest $20 billion on developing petroleum-free motor vehicles and extend expiring tax credits for renewable energy.

Many Republicans, including President Bush, would like to see the moratorium on drilling lifted along the entire Atlantic and Pacific coasts. Some Democrats are unlikely to support any measure that includes increased offshore drilling.

“This is going to be hard to do, we are under no illusion here,” said Sen. Kent Conrad, D-N.D., who led the negotiations on the proposal with Sen. Saxby Chambliss, R-Ga. “But we’ve tried to put something together that is responsible and broad-based and bipartisan, and I think it’s got a shot.”

Senate Majority Leader Harry Reid, D-Nev., is working with the supporters to get it on the floor “as quickly as possible” after the Senate returns Monday, said Reid spokesman Jim Manley.