CONGRESS may soon make a profound change in the American government's balance of power by giving the executive branch something many presidents have sought: a budgetary line-item veto.
Line-item legislation is a major part of the GOP's ''Contract With America,'' and thus its passage would mark a big step for the Republican agenda. Not that the current occupant of the White House would object - President Clinton backs the idea, as do many of his congressional allies.
''Both parties can win when we see a bill on line-item veto that we can support,'' said Senate minority leader Tom Daschle (D) of South Dakota on March 25.
But some lawmakers - both Democrat and Republican - worry that by handing the executive branch a line-item club Congress would be giving away too much institutional authority. Others argue that the veto actually wouldn't work as advertised. And some experts question whether the whole effort is even constitutional.
''It's people angling for short-term advantage with no real focus on the long-term good of the country,'' says Alan Morrison of the Public Citizen Litigation Group.
As of this writing, a bill giving presidents the equivalent of line-item veto power (in budget-speak, ''enhanced rescission authority'') had been cleared for debate and likely passage on the Senate floor. In the House, a line-item provision is attached to a bill that would raise the nation's debt limit.
If the Senate moves quickly, the House may follow suit and pass line-item power as a stand-alone bill. In any case, proponents expect major action by March 29, the deadline for debt limit passage.
Presidents have long sought the flexibility a line-item veto would give them. In basic form, it's a simple idea: Allow chief executives to strike single items they deem wasteful from appropriations bills. Right now, it's all or nothing - either the White House accepts everything in such a bill, or it vetoes the entire thing.
Constitutional concerns have made the current bill somewhat more complex. In essence, its ''rescission authority'' would allow presidents to not spend money for items they don't like. It would also allow the striking of tax breaks that benefit 100 or fewer taxpayers. Congress would be able to override these decisions, but only via a two-thirds vote.
Executive line-item vetoes are a common feature in many state governments. That's one reason ex-Governor Clinton backs the idea - he's seen it in operation before.
To conservatives, the point of a federal equivalent would be reduction of what they judge to be pork-barrel spending. All those dams, bridges, highway projects, and outmoded military bases would suddenly be at risk. According to the libertarian-oriented Cato Institute, a line-item veto might save the US $5 billion to $10 billion a year.
That's all well and good, say critics, but it won't really do anything to balance the budget. Big entitlements such as Social Security and Medicare would be largely beyond the reach of a line-item veto, as would interest the US must pay on the current national debt.
Thus, the most important effect of line-item- veto legislation might be the shift it would cause in Washington's balance of forces. The presidency would win; Congress would lose. It is surely no accident that presidents as far apart politically as Ronald Reagan and Bill Clinton have supported line-item-veto legislation.
Congressional traditionalists such as Sen. Robert Byrd (D) of West Virginia vehemently object to such a transfer of power. Other critics think that the current effort is a clear attempt to change the system of federal government as laid out in the Constitution and remains illegal even in its ''enhanced rescissions'' form.
Alan Morrison of Public Citizen says that if line-item legislation passes, his organization will test it in court. A similar lawsuit brought down the so-called Gramm-Rudman spending-cut legislation of the 1980s, he points out.
''I myself am concerned about accretions of power to any branch of government,'' says Mr. Morrison.
Other experts think the effect of a line-item bill might be more neutral. It's true that the president's power to strike individual items would be enhanced, says Gary Jacobson, a congressional scholar at the University of California at San Diego. But at the same time Congress would be relieved of a certain necessity for institutional self-control.
Lawmakers might be free to lard appropriations bill with all the pork they wanted, secure in the knowledge that the president would veto egregious items, Mr. Jacobson says. They'd get credit for trying to help the folks back home - while the president would become the nation's parsimonious accountant in chief.
Furthermore, Congress might find it easy to skirt line-item legislation in its current form. As the nation's chief lawmaking body, any power the legislature specifically grants it could just as easily specifically take away. Lawmakers thus might be able to pass appropriations bills with riders that say ''no part of this legislation is subject to enhanced rescission authority.''
Whatever happens, line-item power won't take effect anytime soon. Clinton and Senate majority leader Bob Dole agreed last week that Jan. 1, 1997, would the line-item starting date - just before one of them stands up before the west front of the Capitol and takes the next presidential oath of office.