With near-record deficits on the horizon, a senior House Republican says he will push for a constitutional amendment that would force Congress to balance the federal budget.

"Without that kind of discipline, I'm afraid that we'll have deficits as far as the eye can see," said Rep. Jim Sensenbrenner of Wisconsin. His amendment would include an exception for war or national emergencies.

Although even allies view his effort as a long shot, Sensenbrenner plans hearings to help flesh out details such as a reasonable deadline for a balanced budget.

The White House projected this week that budget deficits will leap to $200 billion to $300 billion in each of the next two years. That figure doesn't include any spending on war or President Bush's proposed $674 billion tax cut over the next 10 years.

Sensenbrenner, chairman of the House Judiciary Committee and one of the most fiscally conservative members of Congress, argued the budget could be balanced by cutting back on spending. A prominent economist questioned the feasibility of that.

"I don't see how you can possibly do it in the foreseeable future without raising taxes or without major cutbacks in defense spending," said David Wyss, chief economist at Standard & Poor's. Either, he said, would be a mistake.

Sensenbrenner, who supports the president's tax cut plan, takes the administration's view that the tax cuts will stimulate the economy and increase government revenue. Democrats argue the plan will swell deficits.

In a statement, White House spokesman Scott Stanzel said President Bush supports a balanced budget amendment and is working to get there by restraining spending.

"The president also believes that protecting the lives and liberties of the American people may demand temporary borrowing," Stanzel said, "which is why he believes a balanced budget amendment should include exceptions for war, emergency and economic recession."

The last time a balanced budget amendment came up for a vote, in 1997, it came one vote short of the two-thirds needed for passage in the Senate. But Sensenbrenner is optimistic this time around.

"The discipline of a constitutional amendment - the need for that - has now sprung up," he said.

Sen. Larry Craig, an Idaho Republican, has introduced a balanced budget amendment in the Senate. But even supporters say it will be difficult to win passage there.

"I doubt very much it could get through the Senate," said Robert Bixby, executive director of the Concord Coalition, which wants the Constitution amended to ensure a balanced budget.

Should both houses pass a constitutional amendment, it would have to be ratified by three-fourths of the state legislatures.

Ross Baker, a political science professor at Rutgers University, predicts a tough battle.

"Many states would have a real problem with it," he said. "They depend on the flexibility of the federal government to help them."