WASHINGTON (AP) _ Budget analysts are looking into a possible unintended consequence of the line-item veto law: President Clinton might find the power suddenly suspended if the budget gets balanced.

Although Congress and Clinton recently agreed on a budget deal to eliminate the annual deficit by 2002, some economists suggest it could happen perhaps as early as next year because of the thriving U.S. economy.

The line-item act, which Clinton used for the third time Tuesday in canceling $144 million in projects from a defense spending bill, requires him to use the saved money to reduce the deficit rather than spending it on other projects.

With no deficit, he would have no line-item power, the theory goes.

``We tend to believe that's the case, based on the purposes of the line-item veto that is outlined in the law,'' said Larry Haas, spokesman for the White House Office of Management and Budget. ``That's the best sense that we have.''

Budget Director Franklin Raines said Wednesday he has not examined in detail whether an early budget surplus would cost Clinton his line-item veto powers. But he told a reporter: ``I wish I had that problem.''

The bipartisan Congressional Budget Office dropped its fiscal 1997 deficit estimate this month to $23 billion _ about $100 billion less than it and the Clinton administration projected earlier this year. Fiscal 1997 ended Sept. 30.

``There's a chance that, if all the planets stay in alignment, as they have for the last two or three years, that we could have a small surplus next year,'' said Robert Reischauer, former CBO director.

Such a possibility wasn't a consideration either when the line-item veto was put in the Republicans' ``Contract With America'' in 1994 or when the law was enacted last year. Then, annual federal deficits of over $100 billion stretched as far as the eye could see.

Then Clinton and the GOP-led Congress struck a deal last summer to balance the budget by 2002.

Furthermore, continued low unemployment, low inflation, modest interest rates and the still highflying stock market have helped to push down the deficit faster than expected.

Roger Brinner, chief economist for DRI/McGraw-Hill, a national private forecasting service, said he doubts the budget will be balanced before 2002, but ``If the Fed only slightly taps the brakes, and Congress remains restrained on spending, they really are set to produce a balanced budget.''

Opponents of the law aren't waiting for a balanced budget to try to stop Clinton's line-item veto pen.

The Supreme Court in June rejected a challenge by six members of Congress, saying they lacked legal standing since they had not been hurt by the then-unused legislation. But Public Citizen, a nonprofit public-interest advocacy group, is preparing a new legal assault.

Attorney Allan Morrison of the Public Citizen Litigation Group, a lawyer in the lawsuit brought by the Congress members, said projects vetoed by Clinton _ 38 from a military construction bill earlier this month and 13 defense projects Tuesday _ are being scrutinized.

``We haven't quite figured out who the right plaintiffs will be,'' Morrison said. But he said they would include ``someone who is a pretty clear direct beneficiary of a project'' canceled by a line-item veto.

Several lawmakers have introduced bills to repeal the line-item veto.

Sen. Robert C. Byrd, D-W.Va., among the six original plaintiffs, is a leader in the repeal effort. He calls the law ``one of the most shocking abdications of duty that members of Congress have committed.''