WASHINGTON (AP) — Congressional Republicans are rallying behind a long-shot bid for a constitutional amendment requiring a balanced budget. But they're divided over conservatives' efforts to demand its passage as their price for backing any increase in the government's borrowing limit.

Right in the middle of their brawl with President Barack Obama over extending the debt ceiling and hacking trillions from projected deficits, GOP leaders are forcing House and Senate debates next week over similar amendments requiring the budget to be balanced, starting no sooner than five years from now. Reflecting tea party clout, both measures would also sharply curb Congress' ability to raise taxes and spending.

Constitutional amendments require two-thirds majorities to clear each chamber of Congress, meaning it will be difficult for the GOP to prevail. Republicans hope the debate will highlight their commitment to smaller government and — with polls showing public backing for a budget-balancing amendment — provide fodder to embarrass opponents in next year's elections.

"It certainly will show who's really serious about trying to get spending under control and who isn't," said Sen. Orrin Hatch, R-Utah, a leading sponsor of the Senate amendment, which is backed by all 47 Republican senators. "If that's all it accomplishes, it will be a good thing."

Some GOP lawmakers want to go further, saying that unless Congress first approves a balanced budget amendment, they won't vote to increase the $14.3 trillion ceiling on federal borrowing. The Obama administration says that must happen by Aug. 2 to avoid a catastrophic first-ever federal default.

Supporters of that linkage rank among Congress' most conservative lawmakers, many of whom were unlikely to vote to extend the debt limit anyway. Even so, the move underscores fault lines between the GOP's most right-leaning segments and the rest of the party, even as Obama and congressional leaders see if they can salvage a compromise over the debt.

"It shows how typically weak most politicians can be when it comes to these sorts of issues," tea party-backed freshman Rep. Joe Walsh, R-Ill., said of the scant support for conditioning a debt limit extension to passage of a balanced budget amendment. "This is serious business. I don't think most Democrats understand how serious the spending crisis is, and unfortunately I don't think most people in my party yet do."

As of Wednesday, 12 senators and 36 House members had signed a pledge promising to oppose any debt limit increase unless there are deep spending cuts, budgetary caps that enforce limits on spending, and congressional passage of a balanced budget amendment. Sen. Mike Lee, R-Utah, has introduced legislation cutting spending and requiring approval of a balanced budget amendment before the debt limit can be increased, and House Republicans plan to unveil a similar measure on Thursday.

The "cut, cap, balance" pledge, which is being lobbied by scores of conservative and tea party organizations, has been personally opposed by conservative House Majority Leader Eric Cantor, R-Va. Since Democrats have enough votes to defeat a balanced budget amendment, Cantor says he doesn't want to sign a pledge that could therefore force him to oppose a debt limit agreement he might otherwise favor.

Twenty Democrats would have to vote for the amendment for it to receive the 67 votes needed to clear the Senate, which seems unlikely. Democrats are likely to propose their own less restrictive version, as they did in 1997 when a GOP amendment failed by one vote.

The House, where 290 votes will be needed for approval, has 240 Republicans.

As next week's showdown approaches, heavy hitters on both sides have begun weighing in. White House spokesman Jay Carney said Wednesday that a balanced budget amendment is "about ducking responsibility rather than taking our challenges head on." House Speaker John Boehner, R-Ohio, said the measure would ensure that "spending restraints are set in stone."

Republicans say the amendment would force lawmakers to confront growing federal deficits expected to easily exceed $1 trillion once again this year. And, they say, it would make them do it in a fiscally responsible way by requiring approval by two-thirds of the House and Senate to raise taxes or to let federal spending exceed 18 percent of the overall economy, which this year is about $15 trillion.

"The point is to live within your means," said Rep. Bob Goodlatte, R-Va., chief sponsor of the leading House version.

Critics say a balanced budget amendment is little more than political posturing that impresses voters but still leaves lawmakers facing painful decisions about which programs to cut or taxes to increase.

"Politicians use them to sound like they're doing something substantial on the deficit when in fact they're not," said Robert Bixby, executive director of the nonpartisan Concord Coalition, which advocates balanced budgets.

Democrats, who voted strongly against balanced budget amendments the last time Congress considered them in the 1990s, seem even less inclined to support them now.

They especially dislike the new provision limiting expenditures to 18 percent of the overall economy. Government spending has not been that low since 1966, when Medicare and Medicaid, the giant health insurance programs for the elderly and poor, were just starting and the U.S. population was younger and smaller than today.

"Maybe they haven't heard about the baby boom generation," said Sen. Kent Conrad, D-N.D., chairman of the Senate Budget Committee, noting the added federal costs those 77 million Americans are incurring as they begin to retire.

In another indication of Democratic skepticism, Rep. Mike Ross, D-Ark., a leader of the two dozen "Blue Dog" moderate Democrats, said the provision capping government spending suggested that Republicans are aiming to force cuts in Medicare and Social Security. Sen. Ben Nelson, D-Neb., a moderate facing a difficult re-election battle next year, said he favors the concept of a balanced budget amendment but worried about Medicare cuts the GOP version might force.

Republicans say they want to strengthen Social Security and Medicare.

Goodlatte's balanced budget amendment has 133 co-sponsors, nearly all of them Republicans, according to the congressional database. A less stringent version by Goodlatte that is identical to one that passed the House in 1995 — without this year's restrictions on tax increases and spending — had 221 co-sponsors.

Constitutional amendments do not need the president's signature. Once they pass Congress, they must be approved by three-quarters of the states.