IN what has turned out to be a difficult year for governors throughout the United States, given the recession, a long-established tool has turned out to be a powerful ally for the chief executives in reaching budget agreements: the veto.Indeed, gubernatorial vetoes have been flying fast and furious of late, and not just regarding state budgets. In Louisiana, for example, Gov. Buddy Roemer (D) recently vetoed that state's restrictive new abortion law. The Legislature subsequently overrode the veto, the first time in this century that Louisiana's Legislature has successfully done so. All states except for North Carolina currently allow their governor to wield a veto - the ability to strike down legislation the governor deems unacceptable. Most states also allow the governor to use a line-item veto - that is, strike down parts of a measure enacted by the legislature. Even US presidents don't have such leverage, since they lack the line-item veto. In recent weeks, governors in such states as New York, New Jersey, California, Massachusetts, Washington, Maine, and Illinois have either used their veto power, or threatened to use it in battles over budget plans or involving other high-profile political issues. On Monday, for example, New Jersey Democratic Gov. James Florio vetoed a bill enacted by his own Democratic-controlled Legislature that would substantially weaken the Garden State's landmark ban on assault weapons, including Uzis and AK-47s. But Governor Florio's use of the veto is modest compared with that of his immediate neighbor. New York Gov. Mario Cuomo (D) has discovered the firepower of the veto. On just June 10 alone, Governor Cuomo used the line-item veto 384 times to strike down measures that would have led to a $937 million state budget deficit. Prior to that, Cuomo had used the veto only 547 times in his entire nine years in office, according to Cuomo press officer Terry Lynam. "We never like to use the veto, but the governor's hands were tied," says Mr. Lynam. "Wall Street bond rating agencies were standing by" and watching budget deliberations in Albany with concern, Lynam notes. Cuomo was determined that the budget would be balanced, as required by state law, thus keeping New York's current bond ratings intact. When bond ratings are reduced, as has just occurred in New Jersey, interest rates on debt issues tend to go up, thus eventually costing the state more money in borrow ing charges. As it turned out, New York's bond ratings were left unchanged, following final enactment of a $52 billion budget for fiscal year 1991-92. "Governors have always used the veto in special cases, such as involving the death penalty, or abortion. But they are now using it more in the fiscal area," says Raymond Scheppach, executive director of the National Governors' Association in Washington. The use of the veto is "positive," he says. "The mere threat of a veto forces some resolution" of an issue. Of the 50 state governors, 20 are new to office, says Mr. Scheppach. Yet, they have come to power at a moment of "enormous economic difficulty; they don't have the time to get out front on political issues and go around the state building support for their positions." Thus, the use of the line-item veto becomes all the more important. In the case of New York, for example, Cuomo had only used the line-item veto 22 times prior to June 10 on economic issues, Lynam says. In New York, as in most states, it takes a two-thirds majority of lawmakers in both houses to override a veto. Cuomo has never been overridden on a veto, says Lynam. Not all political scientists are sanguine about the use of the veto. "The veto is an invitation for stalemate, as has been occurring at the federal level" says Demetrios Caraley, chairman of the political science department at Barnard College. Used on high-profile issues, such as the death penalty and abortion, the veto can produce decisive action, Professor Caraley notes. But on economic issues, a veto seldom helps overcome differences between the executive and legislative branches, he says. After the veto, the two sides "still have to negotiate a compromise." Sometimes the too-rapid use of a veto can backfire. In Washington State, Gov. Booth Gardner (D) recently vetoed a $1.7 million item to rebuild a dam site in the state's mid-central region. Unfortunately, the dam creates a lake for a summer camp - for disabled children and their families. The governor, who had been caught up in the legislative rush to produce a budget agreement, hadn't meant to veto that particular project.