A POLITICAL FAILURE of historic magnitude is developing here in Washington this summer. Both the White House and the House of Representatives have repeatedly given thought to a serious attack on the budget deficit -- and have repeatedly decided that they'd rather not. The Senate has now put on the table a new proposal that, among other things, would impose a stiff tax on imported oil. It could accomplish the necessary feat of getting the deficit below $100 billion a year by 1988. But its chances are not brilliant, and the consequences of failure will be drastic. The costs will not be paid by the Reagan administration, which has no more elections to win or lose, but by all the people throughout this country and the world on whom the weight ofeconomic break will fall.

The Senate proposal is probably the last chance for any substantial reduction of the budget deficit this summer -- and if nothing's done this summer, noth will be done before the next presidential election. Next year is an election year, never a good time for tax increases. And after that? It will be the second half of the president's second term. Ninth inning home runs are rare in presidential politics.

Whose fault is the present deadlock? It inevitably lies primarily with the president. He instigated the oversize tax cut of 1981 as part of a great strategy supposed to send savings, productivity and output all soaring. None of that has happened, and Mr. Reagan has steadfastly refused to come to terms with that failure. Instead he keeps fighting off tax increases while the debts mount.

Much responsibility also belongs to the House Democrats. Their adamant and emotional defense of the Social Security cost-of-living increases is a disservice to the country. If they and the president cannot get together on some variant of the Senate proposal, and do it within the next 10 days, the odds will shorten dramatically on a series of highly unpleasant possibilities.

The federal deficit and the Treasury's constant borrowing are keeping interest rates unusually high. The conventional wisdom is that the federal government will eventually try to erase these debts with inflation. But that won't work. The financial markets are dominated by people who lost a great deal of their own and their clients' money in the late 1970s by underestimating inflation, and they won't make that mistake again. At any sign of rising inflation, interest rates will go shooting upward as lenders scramble to protect themselves. Economic growth, already faltering in this country, will drop farther.

At that point the country will probably be forcefully reminded that its present prosperity depends crucially on the money that it is borrowing from abroad at a rate of $120 billion a year. If the foreign lenders begin to get nervous and pull back, the dollar exchange rate will drop and inflation will accelerate while interest rates take another leap upward. Then you will begin hearing more about trouble in the banking system, and the burdens of the indebted Latin countries will become truly intractable. There you have the formula for an economic misfortune that goes well beyond the scale of any conventional recession.

None of these things need happen. But a failure to enact the Senate proposal, with strong and explicit presidential support, will sharply increase the chances of a real disaster. Failure to act now, before the recess, will greatly strengthen the possibility that, several years from now, Americans will cast a heavy judgment on the president and Congress that wasted the summer of 1985 in petty maneuvering for partisan advantage, at a time when disaster lay directly and visibly ahead of them.