IN SPITE OF President Bush’s almost unprecedented reluctance to use the veto power conferred by the Constitution — on March 23, Bush will have served longer without issuing a veto than any President since Jefferson, who vetoed nothing in two full terms — he says the nation needs, and implies that he would robustly use, a line-item veto power that Congress can and should give him. But both the “can” and the “should” are problematic.

The word “veto” is not in the Constitution. It says “every bill” passed by both houses of Congress must be “presented” to the President, who must sign “it” or return “it” to Congress. The antecedent of the pronoun is the entire bill, not bits of it. As President Washington understood: “I must approve all the parts of a bill, or reject it, in toto.”

That did not matter then: The only appropriations bill passed by the First Congress in 1789 was just 142 words long. Besides, early Presidents, according to historian Forrest McDonald, considered appropriations “permissive, not mandatory,” and effectively exercised a line-item veto, as when Jefferson refused to spend $50,000 for gunboats he deemed unnecessary.

Forty-three governors have, and many Presidents have coveted, the power to veto line items. And the Presidential veto power has been partially vitiated by big government — by Congress presenting Presidents with 11 elephantine appropriations bills that make vetoes messy.

In 1996, a Republican-controlled Congress gave President Clinton the power to cancel items that Congress could re-pass in a stand-alone measure. If the President then rejected that, Congress had to muster two-thirds majorities in each house to override him. But in 1998, the Supreme Court frowned. It said canceling is indistinguishable from repealing, which is legislating — writing, not executing laws.

Indeed, the 1996 act made the President the potentially dominant legislator, able to treat a bill as a cafeteria from which he could take whatever he liked. The Constitution does not empower Congress to yield its powers. And a perhaps insoluble and hence disqualifying problem with the line-item veto is this: Legislation, as truncated by a President using a line-item veto, might never have attracted a congressional majority.

Not only is the constitutionality of the line-item veto questionable, so, too, is the veto’s utility as a restraint on spending. Arming Presidents with a line-item veto might increase federal spending, for two reasons.

First, Josh Bolten, director of the Office of Management and Budget, may be exactly wrong when he says the veto would be a “deterrent” because legislators would be reluctant to sponsor spending that was then singled out for a veto. It is at least as likely that, knowing the President can veto line items, legislators might feel even freer to pack them into legislation, thereby earning constituents’ gratitude for at least trying to deliver.

Second, Presidents would buy legislators’ support on other large matters in exchange for not vetoing the legislators’ favorite small items.

During the two-year life of the line-item veto, Vice President Gore promised that President Clinton would use the bargaining leverage it gave him to get legislators to increase welfare spending.

The line-item veto’s primary effect might be political, and inimical to a core conservative value. It would aggravate an imbalance in our constitutional system that has been growing for seven decades — the expansion of executive power at the expense of the legislature. This ongoing development has been driven by wars hot and cold, and by today’s, which is without a foreseeable end.

Time, and perhaps the Supreme Court, will tell whether the President’s proposed line-item veto — Congress would have 10 days to ratify or oppose his proposed cancellations — passes constitutional muster. Sen. Jim DeMint, R-S.C., thinks the President can unilaterally erase much “earmark” spending — $52.1 billion in fiscal 2005 — by directing executive branch officials to ignore spending that is ordered by congressional committee reports but is not included in the text of the actual appropriation bills.

In any case, about 62 cents of every dollar the federal government spends automatically goes to entitlements (54 cents) and debt service (eight cents). Another 21 cents are for defense and homeland security. The line-item veto concerns the remaining 17 cents. That is not trivial: Savings always come at the margin. California Gov. Ronald Reagan used his line-item veto to cut an average of 2 percent from spending bills. The governor of Texas from 1995 through 2000 used his line-item veto on bills totaling $265.1 billion — cutting just .043 percent from those bills he said reflected his state’s conservatism.

George Will’s e-mail address is georgewill@washpost.com.