THE SPENDING issue is as much talked about as the weather and almost, if not quite, as unaffected by discussion. But Dennis Ippolito, an Emory University political scientist, has at least dispelled some of the fog.

Congressional efforts to control spending are almost as old as Congress and their efficacy has varied. But the current chapter begins with the Budget Control and Impoundment Act of 1974. It was, Ippolito shows, the expression of two distinct impulses.

When the act was pending, congressional conservatives shared a sense that the budget was out of control. Liberals and some other conservatives resented the way in which presidents were trying to control it. By failing to coordinate the yearly bills passed by various authorizing committees, Congress, it was felt, was in danger of forfeiting its constitutional control of the spending power. The sense of that danger became acute after the 1972 election when Richard Nixon moved boldly, even brazenly, to "impound" billions of dollars in appropriated funds for reasons of policy as well as economy, meanwhile taunting Congress to enact a spending ceiling.

The 1974 act, born of these two perceptions, produced "partial victories," as Ippolito says, for both. It set up a new congressional budgeting process. It also established a "budget bureaucracy" (the two budget committees, one for each house, and the Congressional Budget Office) that employs 350 people and costs about $20 million a year.

There are benefits. The act regularized in law the disputed power of presidential impoundment. Now permanent impoundments ("rescissions") of appropriated funds may occur only if Congress approves, temporary ones ("deferrals") only if neither chamber objects. The Congressional Budget Office, meanwhile, has given Congress an arm of budget and policy analysis rivaling that available to presidents.

The Senate budget committee, for its part, has disciplined spending to a degree. Ippolito credits its success primarily to Edmund Muskie, who gave up a seat on the Foreign Relations Committee to become its first chairman. Muskie's prestige, stamina and sense of the committee's institutional importance (all too rare in either house) gave it a good start. Moreover, the ranking Republican member, Senator Henry Bellmon, helped. It has been a different story, so far, on the House side. There have been several chairmen, the committee's deliberations have often had a fiercely partisan flavor, and the policy line taken by its Democratic members tends to be set by the House leadership.

Whatever the institutional pluses, it would be hard to argue that the Budget Act has helped control aggregate spending. In the five fiscal years since it passed, in fact, spending and debt have risen just as rapidly in percentage terms as in the five fiscal years before it.

While outlays and debt went on rising, the Budget Act neither freed Congress from so- called "uncontrollable" (legally-mandated) spending; nor, which comes to the same thing, did it afford Congress a means of "reordering" budget priorities. In recent years, with a sharp turnabout following the end of the Vietnam war, budget proportions allotted to defense and "human resources" have remained constant. (In 1981 defense claimed 25.1 percent, human resources 52.6, a 180-degree reversal from 20 or 30 years ago when the proportions were almost exactly the other way around.)

Even so, liberal rhetoric--and the more insistently so since the Reagan administration moved to restrain budget growth--often suggests that the human resources function is being starved. Ippolito shrewdly observes that "the liberals' current discontent . . . may be the inevitable result of their past success. By ensuring automatic spending for social welfare, liberals have left themselves little to do. . . . The federal budget is, more than ever, a social welfare document, but present-day liberals apparently get precious little satisfaction from it."

The more important institutional dispute, however, is not how Congress apportions tax resources but how it might live within its actual means. This the Budget Act has not accomplished. The spending ceilings fixed in the second and "final" yearly budget resolution are often raised by third resolutions. "Supplemental" appropriations and "off-budget" expenses have become favorite devices for evading theoretical limits on spending. The institutional machinery is adjusted to political need, not vice-versa.

And where does the pressure to spend come from? Ippolito assembles impressive evidence that while voters and politicians deplore excessive spending in general, specific programs remain popular. Their popularity forces Congress to practice institutional duplicities.

Meanwhile, driven by inflation, the public sector swells and the great unresolved question is this: What proportion of the national product should government control through the budget? At all levels, federal, state and local, it is now almost 40 percent. If that proportion is excessive and stifling to private initiative, as many argue, how may Congress overcome political pressures to spend and make expenditures fit revenues?

Ippolito concludes that, with the failure of the Budget Act, more drastic medicine is needed. He believes that the only realistic solution is a constitutional amendment featuring a restrictive formula that would limit the budget to a fixed percentage of GNP. Many of us have been skeptical of that solution, but Ippolito makes a strong case for it. His careful responses to the usual objections cannot be lightly dismissed. Indeed, in addition to providing an excellent primer for the mystified taxpayer, he has filed a persuasive brief for a solution to runaway spending that now seems as inevitable as it will be unwelcome.