WASHINGTON (Reuters) - A Democratic-backed bill to rein in energy market speculators blamed for high crude oil and gasoline prices cleared a U.S. Senate procedural hurdle on Tuesday, but final passage of the legislation remained uncertain. Supporters mustered far more than the 60 votes needed in the 100-member Senate to proceed with the measure, with 94 senators voting "yes" and none against. Yet Republicans may still block a vote on approving the bill unless amendments are added to increase U.S. oil production, such as expanding offshore drilling and developing oil shale fields in the West. The Senate legislation would require...