UPDATE 1-Biden to meet Democratic lawmakers on Capitol Hill

(Updates with background)

WASHINGTON Aug 1 (Reuters) - Vice President Joe Biden will meet with Democratic members of the House of Representatives and Senate on Monday, ahead of vital votes on a controversial deal to lift the U.S. debt limit.

The White House said Biden, who has been at the heart of negotiations to raise the $14.3 trillion borrowing limit and avoid a devastating U.S. default, will meet senators at 11 a.m. (1500 GMT) and House Democrats at 12 noon (1600 GMT).

Biden's presence will be important to rally support for the deal. Liberal Democrats are very unhappy the measures to raise the borrowing ceiling by $2.4 trillion contain no guarantee of steps to lift tax revenues.

Critics warn this could put the burden of deficit reduction on spending cuts alone, potentially hitting programs cherished by Democrats like Medicare that would disproportionately hurt the elderly and the poor, while letting the wealthy off the hook. (Reporting by Alister Bull; Editing by Philip Barbara)