Sometime in the next year or so, Congress may get a surprise package in the mail - an order from the states to call a constitutional convention. Last Thursday, almost unnoticed by official Washington, Missouri became the 32nd state to pass a resolution calling for a constitutional convention to consider an amendment requiring a balanced federal budget. If two more states join the chorus, Congress will have no choice but to call such a meeting of delegates from the various states.
Of course, it isn't a foregone conclusion that the convention will be held. Over the past 20 years, concerted efforts to force constitutional conventions on other subjects have come close to success, only to fail in the end.
But 32 states are the most that have ever voted for such an unprecedented action.
''We have a good chance of reaching 33 states by early next year,'' claims David Keating, an official of the National Taxpayers Union, an organization pushing hard for a balanced budget amendment. ''Then we'll get a great deal of attention.''
To put all this in historical perspective, consider that the last US constitutional convention was held in 1787, two years before George Washington was elected president.
Since then, all proposed amendments to the Constitution have been suggested by Congress, after being approved by a two-thirds vote of both houses. But there is another legal method of proposing constitutional change.
''. . . on the Application of the Legislatures of two-thirds of the several States, (Congress) shall call a convention for proposing Amendments . . . ,'' says Article V of the Constitution.
The convention method has never been invoked successfully, though Congress has received hundreds of requests from states for conventions on everything from polygamy to prohibition. Pressure from a mounting pile of state resolutions probably forced Congress to propose the 17th Amendment, eventually ratified by the states, which provides for the election of senators by popular vote.
Until now, the closest the United States has wandered toward a constitutional convention was in the mid '60s, when 32 state legislatures called for a convention dealing with legislative apportionment. From that high mark, the issue gradually slipped into obscurity.
The drive to insert a balanced budget amendment into the Constitution has now also collected the signatures of 32 states.
Last year, supporters of the balanced budget amendment concentrated on Congress. The issue had a brief but spectacular front-page career, passing the Senate but finally falling short on a House vote.
As far as most of Washington was concerned, that was the end of the amendment. But supporters say their drive for a convention on the budget issue will either force Congress to act, or succeed in its own right.
In eight states, a resolution calling for a balanced budget convention has passed one legislative house, but not the other. Only two of those states must complete action to force Congress's hand, points out NTU's Keating.
But congressional staffers critical of the amendment say its momentum in the states has slowed considerably. Twenty-two states passed resolutions on the issue in 1978. Eight more acted in 1979. It then took three years before the 31 st state, Alaska, fell in line; Missouri followed 18 months later.
The drive for a balanced budget convention, say these staffers, may be hanging by its fingertips, about to descend into obscurity.
In any event, the convention push raises the question of why Capitol Hill has never passed legislation outlining what to do if the call for a constitutional convention succeeds.
Ten years ago an American Bar Association study group concluded that constitutional conventions were an uncharted legal area. It recommended that Congress pass laws that would, for example, create formats for state resolutions and limit the convention to the subject called for by the states.
Despite numerous attempts, Congress has not passed such a law. Sen. Orrin G. Hatch (R) of Utah has reintroduced a convention procedure bill. Without guidelines, any convention would ''become bogged down in constant litigation, partisan political decisions, and constitutional uncertainty,'' he has said.