IT'S JUST A blip on the radar back east, but in California it was front-page news. The state Supreme Court has thrown off the November ballot an initiative aimed at making that state the 33rd to call for a constitutional convention to consider an amendment requiring a balanced federal budget. As jurisprudence, the court's decision is debatable. The U.S. Constitution says that only the legislatures can call for a constitutional convention; the initiative's backers, to get around that, said that if the legislators didn't so vote, their salaries would be cut to zero. We see through that subterfuge, said the court in effect; and anyway, it went on, the subject of this initiative is a resolution not a law, and so it's not authorized by the state initiative law. Republicans have some ground for believing that this 6-1 Democratic court acts to take issues away from the voters only when they're likely to be resolved the Republicans' way. Still, the result is welcome.

The court's decision slows down, but does not necessarily halt, the dangerous move toward a constitutional convention. Some 32 states -- only two fewer than the required 34 -- have already issued such a call; some have tried to rescind their actions, but no one is sure what the constitutional effect of such an action would be. No one can be sure, either, what would be within the purview of the constitutional convention if 34 states did sign up and a convention were called. Could it repeal the Bill of Rights? Could it abolish the jurisdiction of the Supreme Court? Could it change the dozens of settled constitutional arrangements on which individuals and governments have relied for nearly 200 years?

Maybe, maybe not, say the experts. Not to worry, say those who seek the convention; even if the convention could do mischievous things, the states don't have to ratify them. Fine and dandy. Except, of course, they might. And in the meantime everyone's attention would be diverted to these purportedly vain deliberations. And the amendment sought -- the one that would supposedly guarantee a balanced budget and put the nation on fiscal autopilot forever -- would be either economically disastrous or, more likely, ineffective and easily bypassed.

President Reagan is trying to make the so-called balanced budget amendment a campaign issue. But the president already has it within his constitutional power to propose a balanced budget, and the Congress already has it within its constitutional power to adopt one. Those who want a balanced budget should join those of us who want a budget considerably closer to balance and set out for all to see the changes they want in government spending and tax laws, rather than continuing on the dangerous diversion of threatening constitutional mayhem.