WHEN HISTORIANS of public policy in the 1970s judge the performance of the intellectuals, they are likely to conclude that whirl was king. In the Neo-Georgian brick halls at Harvard, in book-lined apartments of Manhattan, prominent and certified thinkers agree on only one point: There is little or no agreement on issues of major consequence.

The consensus that marked the first 25 post-World War II years has been shattered. At home, there had been a mainstream academic view, a belief that Keynesian economic policies could repeat indefinitely the hat tricks of more or less steady growth in goods and services, high employment and generally stable prices. An intractable and worsening inflation has factured this. With it, too, has fallen the belief that the dividends from increasing growth could create Cotton Mather's vision of Heavenly Cities.

The thinkers are in similar difficulties on foreign policy, whether they try to design an appropriate response to the Soviet Union, calculate what support, if any, to give threatened and distant regimes, or draw up a blueprint to lead Asian and African nations through the stages of growth.

Talks with noted intellectuals in Cambridge and New York, in fact, not only confirm that the mainstream of ideas has split into dozens of rivulets, but that in some areas it has dried up altogether.

At least since Franklin Roosevelt, presidents have turned to academics for counsel, confident of finding a "brain trust" to inject fresh ideas into stale bureaucracies, to provide at least a gloss of coherence for great issues. But today Washington often seems the mirror image of the intellectuals, alternately conciliating and infuriating Russians, spurring and dampening the economy. Dissonance in ideas matches contradiction in policy. One key official here frequently imports academic economists for short tours on his personal staff. "They haven't been worth the plane fare," he remarks. He recalls only one marginal proposal that was useful.

"At cocktail parties, people say, 'Isn't Carter terrible?'" observes Harvard sociologist Nathan Glazer. "I reply, 'Why, I don't know what I would have done.' The cupboard of ideas is bare. If Carter had task forces, I wouldn't want to read their papers. Now there is nothing. No new departures."

John Kenneth Galbraith recalls that, "From the Full Employment Act of 1946 until the late '60s, the great consensus was the consensus of Keynes," the notion that appropriate spending, tax and monetary policies could ensure unbroken prosperity. "Students of economics were taught and then taught Keynes without thought. As long as there was less than full employment, it worked," Galbraith says. But when the economy came under pressure from public and private demands, "putting Keynes in reverse wasn't a solution." So now there is a babel of contending voice - monetarists, neo-Smithians, latter-day Austrians, neo-marxists and more.

Galbraith's "The Affluent Society, published in 1958, was a powerful instrument to promote the notion that wasteful, private outlays robbed public needs of resources, creating squalor. The widely read book helped spur great public spending programs in the cities, for the poor, blacks and others.

Edward Banfield, a Harvard professor of government, was an early and astringent skeptic. Today he observes with satisfaction: "Programs that seemed plausible, that were well-funded and well-administered, didn't produce the results that were wanted. Unintended consequences loomed large."

Banfield ticks off the list of failures he foresaw in his 1970 book "The Unheavenly City": Slum clearance that did nothing for those driven from their homes; public housing that became "a shambles"; training for the unemployed and unemployable that left them untrained and jobless; striving to improve the education of the poorest achievers with little results. "It would cause outrageous hardship to shut off" these programs, Banfield says. His limited solution calls simply for "weaning people away from them" - and more study.

Banfield, in sum, breaches the last line of defense for programs that fared poorly. He denies that they were starved of funds or run by poor administrators. In his view, they never should have existed.

Irving Kristol is a dominant figure in the new school of neo-conservatives, co-editor of The Public Interest, their journal, and Henry R. Luce professor of urban values at New York University. He is resigning his Luce chair, he says,because "I don't have anything to say anytmore. I don't think anybody does. When a problem becomes too difficult, you lose interest."

Robert Nozick, an engaging Harvard philosopher, dazzled the intellectual world five years ago with his "Anarchy, State and Utopia," a difficult but brilliant tract urging the "minimal" state. Now 40, and one of the relatively rare younger intellectuals with a reputation for thinking about public questions, Nozick says:

"I can't believe that those pursuing foreign policy goals will do a good job. If Iran came as a big surprise, how can we be confident [officials] will advance American interests? The amount of mistrust of government is very large - Watergate, of course - and I think it's very good. We no longer trust their good motives and their ability to accomplish things - across the board."

Not long ago, Nozick sat in on an editorial board meeting at Partisan Review, a glory of New York cultural life since the 1930s. The editors, he recalled, were debating what attitude to take toward the shah and his successors. There was no agreement. "We all feel insecure on politics and economics," Nozick remarks. A rising hysteria"

New circumstances, the course of events, are cited by the thinkers as the sources of confusion or retreat. Inflation and Vietnam, Watergate and Agnew, the persistence of slums, poverty and crime - all have shaken consensus and certitude. Galbraith argues that unemployment "is the only thing" that Keynesian techniques can remedy, and inflation inhibits their use.

He and a few others, like Robert Lekachman, are convinced that a new consensus will form around price and wage controls. But so far this is more of a side eddy than a mainstream view.

With a broad grin, however, the retired Harvard economist insists, "Galbraith, as usual, is identifying himself with the masses," and he cites public opinion polls that heavily favor his proposal for controls.

Glazer is one of Harvard's most far-ranging sociologists and the other co-editor of The Public Interest. He thinks economists have not yet fully understood the shattering effect of accelerating prices on the socialorder. "There is a rising hysteria," he says. "It's not left wing or right, but it is very alarming. Saving and forethought become useless. Inflation reaches very far. That is the failure of the macroeconomy and its theorists. Everybody has a stake in stability."

From a comfortable chair in the Century Club in midtown Manhattan, Lekachman, an undoctrinaire socialist and professor at the City University of New York, lists the heavily credentialed economists high in the Carter administration - W. Michael Blumenthal, treasury secretary; Ray Marshall, labor secretary; Charles Schultze, chairman of the president's Council of Economic Advisers; Juanita Kreps, secretary of commerce. "Any sensible politician knows better than to listen to them," he says. "The economists are in substantial disarray. I can understand why Carter listens to Jody Powell instead."

Like Banfield, Lekachman takes some grim satisfaction in the lack of coherence. His last book, published in 1976, was "Economists at Bay: Why the Experts Will Never Solve Your Problems." Inventing problems

At least some of the urban experts are insisting the problems of the cities exist exclusively in the minds of those industriously pursuing solutions. "Most of the problems had been created by people trying to solve the problems," Banfield contends. "They made new and bigger problems. If we let up, that's all to the good. But it is very hard for Americans to recognize there are some problems we can't solve. It would be useful if politicians could say this."

Another Harvard luminary, Daniel Bell, is equally agnostic. In the domestic sphere, he says, "Nobody has any answers he is confident of. If he does, he's a fool."

Bell, a sociologist who enriched the language with his notion of a "post-industrial state" and in 1960 also proclaimed "The End of Ideology" for America, recites some issues that baffle policy intellectuals.

"How do you design a decent housing environment?" he asks. If the government builds housing, it may be wrecked, like the ill-fated Pruitt-Igoe project in St. Louis. If private builders are subsidized, corruption follows. There are no genuine answers to rising medical costs, Bell adds, and nobody knows how to retrain the unemployed for jobs.

Philosopher Nozick notes there was once widespread, humanitarian backing for laws compelling employers to pay a minimum wage. "That looked like something any good soul would support. But now we're told that it produces unemployment among black teen-agers. If that fails, all fails."

Kristol recalls that some White House aides had invited a small group - Glazer was also in it - to propose ways of redeeming a presidential pledge: reviving the wasteland that is the broken and abandoned South Bronx. "We couldn't think what to do," Kristol remembers. "We only know how to build houses, but the problem is jobs, and we don't know how to create jobs for these people."

Irving Howe is one of the great polymaths on the New York cultural scene. A distinguished literary critic and historian, he displays the synoptic grasp of thinkers often found outside the academy, like the late Demund Wilson. Howe's politics are social democratic, to the left of the thinkers discussed here, except for Lekachman. But like the others, he agrees, "We're into disarray."

howe rejects the crude formulas of the new left, such as the dogma that impotence over urban problems is racist, a dismissal of diffculties largely limited to blacks.

He agrees, however, that "there is a decline of good feeling, a social meanness, but it is not actively malevolent. There is an insensitivity, not a hostility. There is an attitude of , 'Oh, let them stay on relief. Just as long as they don't make trouble, we'll pay them.'" Seeking saints and devils

The breakdown of intellectual consensus over foreign affairs is ascribed on all sides to one prime cause: Vietnam. Some mainstream thinkers played a central role in urging, shaping and measuring that conflict. The defeat chastened them.

So has the complexity of a new world in which the communist center has split, divided between Peking and Moscow, in which the non-communist world has seen the rise of Japan and Germany.

Those intellectuals who opposed the war and glorified Hanoi or the great reforms in China have also been forced to think again. Saints and devils are no longer so easily identified.

Bell of Harvard puts it this way: "The Cold War mobilized a lot of people. The American role as the dominant world power after the war mobilized many, too, especially in the universities." But now the calls go unheeded. After Vietnam, as Kristol says, "there is a recognition of intractabilities."

For Galbraith, an early opponent of the war, this is a source of satisfaction, "an inevitable and highly desirable consequence of better information."

"In the '50s and '60s, foreign affairs was delegated to the foreign policy establishment, a very small group of New York lawyers and professional scholars," he remarks. "They created a unity of view on foreign policy which was disastrous. There were the sensitivities of the Cold War, the necessity of Vietnam. Communism was seen as intrinsically wicked, not a social force. Now we reconize that things are more complicated. The speciousness of the particular error, Vietnam, accelerated the process."

To be sure, the dissonance of the intellectuals is not heard everywhere. In a private Manhattan dining room, 10 stories above an atrium filled with trees and plants, McGeorge Bundy, former Harvard dean and national security adviser to Presidents Kennedy and Johnson, is convinced he can still chart mainstream thought. Strictly speaking, Bundy is not a licensed intellectual, not an author of seminal books. But as president of the Ford Foundation, he is a Medici to the thinkers, a patron financing some of their work.

Bundy acknowledges that since vietnam there is a "less dominant" consensus to support the kind of intervention that led the United States to face down the Soviets over their missiles in Cuba and to supply beleaguered Berlin with airlifted supplies.But foreign aid, he asserts, still commands support in Congress and the universities, whatever the difficulties of development. "People come to us with proposals they know we will fund," he says with satisfaction.

At home, "the whole system of services and transfer payments is very much criticized, but it isn't dismantled. We've got a few building blocks for the cities. A good mayor who looks in the right places can get a lot of good advice, and it will be coherent."

"There is great progress" in solving urban problems, Bundy states, "but a lowered level of immediate concern - except for people who do it for a living, like us." A Republican windfall

If important thinkers are deeply divided or confess their impotence, does it make any difference for public policy and politics?

Bundy, who is leaving the Ford Foundation on June 1 to write and teach at NYU,is quick to point out that the Marshall Plan was announced - not invented - at Harvard. However, he adds, the most elqouent attack on McCarthyites was delivered not by a professor but by John Lord O'Brian, a distinguished lawyer. O'Brian, a conservative,spoke out frequently and forcefully in the 1950s against the assaults on personal liberty that had been leveled in the name of national security.

Keynes, with a different vested interest, had a different view from Bundy's. "The ideas of economists and political philosophers," Keynes once wrote, "both when they are right and when they are wrong, are more powerful than is commonly understood. Indeed, the world is ruled by little else. Practical men, who believe themselves to be quite exempt from any intellectual influences, are usually the slaves of some defunct economist. Madmen in authority, who hear voices in the air, are distilling their frenzy from some academic scribbler of a few years back."

As might be expected, today's thinkers are not eager to claim that their lack of coherence helps explain Washington's confusion and equally reluctant to acknowledge that they matter not at all.

In the end, though, they are vocationally compelled to acknowledge that ideas matter, that there is a link between the frequent contradictions in the Carter administration and the void left by those with a reputation for elevated thought on high policy.

Galbraith suggests that the indecision of the intellectuals is a "partial, very limited explanation" of the government's meandering policies. He characterizes the shifts in economic policy, for instance, as the fruits of "good men who are liberal Keynesians but uneasy."

Bell argues that suspicion of government has created a gulf between thinkers and actors. "There was systematic lying by Johnson and Nixon. It built up a mistrust of data and people. There's an awfully high political discount rate, and Carter hasn't yet made himself credible. You don't know what you can believe."

His fellow sociologist, Glazer, is "extremely sympathetic" to the administration's problems. "It's very difficult politically to say nothing works," he points out. "Academics can say it, but so what? What we have to offer is extremely modest."

On the right and on the left, the thinkers agree that the absence of mainstream thought has political consequences and has produced a windfall for Republicans. Kristol, who contributes essays to The Wall Street Journal, thinks that the old consensus was a big asset for the Democrats and particularly their liberal wing. Now "the party with no theory is better off - at least temporarily - than one with the wrong theory."

"The Republican Party has no theory of public policy," he adds. "It simply has instincts and traditions." The new technicians

For howe, his fellow social democrats are up against it. We know we have troubles,but we haven't formulated troubles into issues. Social democratic policies are boring. They don't arouse quasi-religious passions, and this matters in the country of Emerson and Thoreau.

"They [conservatives] have the opportunities. Less intervention. fewer pointy-headed bureaucrate - these appeals have power."

The end of consensus has driven many younger, bright academics into a retreat from public policy. Ambitious economists elaborate elegant mathematical solutions to theoretical problems with little if any relevance to public issues. Sociologists and political scientists devote themselves to testing and evaluating programs and scrupulously avoid a search for fresh answers.

Galbraith describes "the Belmont Syndrome, in which economists commute from pleasant homes in suburban Belmont to their computer, and involve themselves with nothing wider than their families."

Bell says Harvard's sociology department has two unfilled places for scholars under 45. The department can't find anybody with the needed breadth. The jobs "go begging. There are some brilliant hotshots, but they are all technicians. When the world is messy, you fall back either on ideology or technique. Good young people respond to the seduction of technique. It's independent of experience, and you don't have to know much."

All this will provide small comfort to those in Washington grappling with public policy issues. They are deprived of a resource. The best and brightest in New York and Cambridge now retreat to computerized towers. When they emerge, they speak either with muted or discordant voices.

Little blame, perhaps, should attach to the academics. Like harassed politicians, bureaucrats and citizens, they are creatures of the times. A Marx produces his powerful critique against the overwhelming background of a harsh and primitive early Victorian industrialism. A Keynes conceives his general theory when it is evident to every person in the street - if not to fellow economists - that mass unemployment is not a temporary aberration to be cured by cutting wages.

The grteat intellectual breakthroughs rarely precede but are typically the product of events. If answers to problems are found, they are more likely to emerge from experience, from trial and error, than from some startling departures in the learned quarterlies or in the academies. CAPTION: Illustration, no caption, By Robert Barkin-The Washington Post; Picture 1, Nathan Glazer; Picture 2, John Kenneth Galbraith