Voters in the the United States are casting their ballots in midterm elections widely expected to usher in a Republican-controled Congress. Democratic losses could complicate Preisdent Barack Obama's agenda during his last two years in office.

The ultimate decision will be rendered on Tuesday elections, with the final results unknown until 0500 UTC, when the last polls close in Hawaii and Alaska. Obama's Republican opponents already control the lower chamber, the House of Representatives, and are expected to maintain or even extend their advantage there. All 435 seats are up for grabs on Tuesday.

Democrats hope to cling on by their fingernails to the Senate's top posts. Republicans seek to wrest control of the chamber by winning at least six seats and eking out a razor-thin majority that would likely not much change the gridlocked nature of US politics.

Nevertheless, outside interests invested record sums hoping to influence voters one way or the other in the two-party system. In the 100-member Senate, only three seats are held by independents, with the slimmer possibility of a fourth and the longer-shot of a fifth winning on Tuesday.

'Just flat-out failed'

Weighed down by Obama's low approval rating of about 40 percent, Democrats have kept their distance from their president and looked to the costly get-out-the-vote operation in the most competitive Senate races to save their seats and their majority. Democrats also hope to minimize their losses in the 435-member House of Representatives and have worked furiously to reach out to minorities, women and young voters, as well as to defend themselves from Republican attacks.

"The president's policies have just flat-out failed," House Speaker John Boehner said Monday - omitting the fact that his Republicans have themselves not put forth much in the way of successful policy during their four years of controlling half the legislature.

Thirty-six of the 50 US states will also pick governors on Tuesday, with an unusual number of incumbents from both parties appearing to struggle. Wisconsin's Republican governor, Scott Walker, could go down to his Democratic challenger, Mary Burke, after overplaying his hand in his crusade against organized labor. In another hard-fought race, Florida Republican Governor Rick Scott could lose to former Florida Republican Governor Charlie Crist, his immediate predecessor - now running as a Democrat.

mkg/ksb (Reuters, AFP, dpa, AP)