WASHINGTON - The Senate deadlocked Monday on a bipartisan energy bill, with Republicans mounting a filibuster that also is likely to end any near-term consideration of the Keystone XL pipeline proposal that has become a key issue in several critical elections.

The vote Monday - 55-36, mostly along party lines - on a modest energy efficiency bill written by Sens. Jean Shaheen (D., N.H.) and Rob Portman (R., Ohio) ended a long but sporadic attempt to approve legislation that has been ensnared by several controversial side issues amid Republican attempts to attach amendments to the bill. All Philadelphia-area senators voted in favor, except Pat Toomey (R., Pa.), who voted no.

The Shaheen-Portman bill now has become wrapped around Republican demands for several pro-energy proposals that would promote drilling or rein in environmental regulations. Most important, in terms of the midterm elections, the debate seemed at one time to provide the best chance for the chamber to hold a binding vote on the controversial Keystone XL pipeline, because several Democrats running for reelection in conservative states have been pushing for it.

Senate Majority Leader Harry Reid (D., Nev.) gave in to those Democratic requests and said he would allow a vote on a measure mandating that the administration move past its current environmental and legal reviews of the pipeline and ordering that it be approved. But he said the Keystone vote was contingent on first approving the Shaheen-Portman bill without allowing for any amendments on either side of the aisle.

"That's what I want to do. He doesn't want to do it," Reid said Monday evening before the vote, motioning to Minority Leader Mitch McConnell (R., Ky.).

That effort fell apart late last week, Reid said, because Republicans who were supporting the underlying legislation demanded votes on pro-energy amendments.