PRE-ELECTION congressional sessions invite political ploys, and at first glance Speaker Tip O'Neill's latest promise just seems another of them. Mr. O'Neill has promised that, if the president submits a balanced budget, the House will vote on it within 48 hours. Everyone knows this is a promise Mr. O'Neill will never have to deliver on. Everyone understands it's a partisan riposte to the familiar Republican charge that it is the Democrats who prevent the budget from being balanced.

Grant all that. Even so, Mr. O'Neill's promise usefully illuminates the debates over both policy and politics. Note that the speaker doesn't promise to support any balanced budget the president should propose; he just promises to let the House vote on it yea or nay. But before you call Mr. O'Neill a hypocrite, ask yourself this question: Which of the 435 members of the House, all of whose seats are up in November, would vote for a a balanced budget? Far fewer, we wager, on both sides of the aisle, than you will hear ritually praising the balanced budget in the abstract.

The fact is that few in Congress or elsewhere have given much serious thought to what a balanced budget would actually look like. Cut domestic spending all you want, eliminate all welfare programs you don't like, adopt every recommendation of the Grace Commission, take great machete chops at defense -- do all those things until the budget is balanced, and you will come up with something almost every congressman will find in some critical aspect unacceptable. Cut Social Security, and Mr. O'Neill won't even be able to get it to the floor.

Mr. Reagan would rather complain that Congress, or the Democrats, won't cut spending as much as he'd like -- and glide over the fact that he won't say, with minor exceptions, what spending he would cut himself. But Congress has a good reason for not cutting spending further: the American people don't want it done. They want substantial defense spending. They want interest paid on the national debt. They do not want the rest of the federal budget chopped to nothing -- which is roughly what you'd have to do to balance the budget if you kept those first two kinds of spending and allowed no tax increase.