The conflicting ambitions at work in the budget impasse would make it hard to break in any case, and the collision between President Reagan and Speaker Thomas P. O'Neill makes it all but impossible.

No one foresaw such agony when Congress equipped itself with a new "budget process" eight years ago. The Budget and Impoundment Act of 1974 was slated as the ultimate answer to budgetary strife. But the new process eased one irritating problem (the abuse of presidential "impoundment," as Congress saw it) only to produce another: chronic deadlock over the "out-year" deficits that the new accounting system forces Congress to face in its twice-yearly budget resolutions. Meanwhile, the deep economic slump complicates everything. When Congress adopted the "mandated" spending now so difficult to control, everyone thought the end of the Vietnam War would produce surpluses, even a "fiscal dividend."

For further irony, the indexation of mandated payments (federal pensions and Social Security payments) to the consumer price index was viewed as a solidly conservative measure: it would stop the capricious pre- election boosts in Social Security payments that often greatly exceeded inflation. Instead, it combined with inflation to render the social budget "uncontrollable."

But this is far from the heart of the matter. Alone among major democracies, the United States has no mechanism for resolving fundamental budget conflict swiftly and sensibly--conflict that has become the more fundamental with the new priorities of Ronald Reagan. Reagan tax levels and O'Neill spending levels are flatly incompatible. But no means of reconciling them is at hand.

This oddity in the U.S. budget-making system has been the object of compelling analysis for a century or more. Harold Laski, the distinguished British political scientist, gave the problem a workout in his "American Presidency" lectures during the FDR years. Congress and the president, Laski noted, usually work together in harmony when their business is minor, "retail" as he put it, or when there is a major threat "to the foundations of society." Normally, however, "The more positive a president sets out to be, the more unlikely is he to be able to insist upon his primacy," since "the whole drive of the system is against him."

In other words, "The separation of powers becomes the confusion of powers," especially when the budget is at issue. Congress, Laski suggested, should "adopt the kind of self-denying ordinance that has worked so admirably in the House of Commons." Under this self-imposed restraint, single members could not exceed a president's budget requests.

There is, alas, no talk of self-denying ordinances in Congress today. Indeed there is no talk of fundamental readjustment of any kind. There is no machinery for resolving an otherwise irreconcilable budgetary impasse. This means that no central vision informs the federal budget, no intelligible policy shapes it, and no voter knows whom to punish or reward for what finally emerges. The budget negotiators are really dealing with a fundamental institutional disorder as if it were a mere quarrel over politics and money.