* House Democrats oppose short-term debt limit extension
* Bill would suspend pay if lawmakers fail to pass budget plans
* Republicans aim to shift focus of budget battles
By David Lawder
WASHINGTON, Jan 23 (Reuters) - The U.S. House of Representatives on Wednesday began considering a Republican measure to extend the U.S. debt limit for nearly four months but many Democrats vowed to oppose the measure, calling it a gimmick that sets up a new "fiscal cliff."
A test vote to proceed with debate on the measure showed a nearly strict partisan split, with 234 votes in favor and 190 against. Just six Democrats supported it.
The bill, likely to pass both the Republican-controlled House and Democratic-controlled Senate, also was endorsed by the White House on Tuesday. It would avoid an immediate threat of U.S. default by suspending limits on the government's ability to borrow until May 19.
The U.S. Treasury is expected to exhaust all remaining capacity under the $16.4 trillion debt limit sometime between mid-February and early March.
The bill, a shift in tactics put together by House Republicans at a retreat in southern Virginia last week, buys them time to shift the debate over spending cuts from the highly charged - and politically toxic - debt limit to other fiscal deadlines that they see as more productive.
Senate Majority Leader Harry Reid on Wednesday praised the House debt limit measure for not requiring spending cuts and said the Senate would take up the measure upon House passage.
The bill aims to draw Senate Democrats into the debate by requiring the chamber to pass a formal budget resolution by April 15. If either the House or Senate fails to meet this deadline, lawmakers' pay is suspended until they pass a budget.
"The bill we are passing today, we think, will give us the ability to have a debate that will last a number of months about contrasting visions," House Budget Committee Chairman Paul Ryan told a breakfast for reporters sponsored by the Wall Street Journal.
"We see this as a very defining moment for this session of Congress and our caucus on getting a down payment on the debt crisis, on averting it."
But Democrats objected, saying it was irresponsible to set short-term debt limit deadlines that would keep a cloud of uncertainty hanging over financial markets, prompting volatility and higher interest rates.
"This legislation sets up another fiscal cliff, another financial nightmare, another problem for the American people that we should avoid," said Representative Rob Andrews, a Democrat from New Jersey. I urge all members to vote no."
The next fiscal deadlines that Congress must deal with are the March 1 start of automatic spending cuts for military and domestic programs, and the March 27 expiration of funding needed to keep federal agencies and programs operating.