A bid by Democrats in the House of Representatives to toughen the estate tax in President Barack Obama's $858 billion tax cut bill failed on Thursday, giving the plan's prospects for final passage a significant boost.

The House voted down an amendment to impose higher taxes on estates of the wealthy when they die.

The Senate overwhelmingly approved the $858 billion tax bill on Wednesday.

(Reporting by Richard Cowan, Editing by Sandra Maler)