BLACK disappointment with the Carter administration, a low murmur several months ago, has swelled to a crescendo. A key element in the coalition that elected President Carter is becoming estranged from his administration and resentful of its failure to launch a massive attack on the problems confronting black people and the cities in which they live.

What happened to cause this disappointment? Were black expectations so unrealistically enlarged that no administration could meet them? Or have the administration's policies been so inadequate?

In the main, black expectations were realistic. It was generally understood that political and budgetary restraints would prevent total, short-term transformation of our society. But it was also expected that national priorities would be reordered and that major domestic initiatives would be made, inaugurating real and much needed changes.

A refrain of administration spokesmen has been, "We've only been in office six months. Give us time." But the first six months of an administration set the tone for the remainder of the presidential term. There is suspicion that the basic principles that may come to inform all of its domestic policies will be too cautious - a priority on keeping costs down, even where that may mean defeating the goals of a program, premature compromises to make programs palatable to conservative interests and an assumption that the problems of poverty and joblessness have their origins in supposed deficiencies within the poor rather than within an economy that doesn't create enough jobs.

FOR AN administration concerned with morality in public, it is unconscionable to place the burdens for balancing budgets and controlling inflation on the backs of the poorest and most deprived in our society. A civilized society can no longer expect poor people to accept unemployment in order to preserve affluent people's price stability.

Sound national policy requires greater flexibility and innovation on the federal level and the adoption of urgent national priorities to change the social environment in which our people live; an environment characterized by poverty in the midst of affluence; by racial tensions worsened by competition in a scarcity economy, and ny urban deterioration hastened by the erosion of the urban economy.

The first priority of this - or any - administration should be full employment. It is simply not enough to measure progress in this area by lowering the unemployment rate by fractions of a percentage point or by creating several hundreds of thousands of jobs. A decade ago presidential commission endorsed creation of about 5 million jobs to put people to work and to improve public services. That should be a minimum, short-range goal, with the longer-range goal of ensuring that every person able to work has a decent job at a decent wage.

A federal program of public service jobs, public works and incentives to the private sector should be tied to definite numerical goals and a rigid timetable. It cannot be conditioned on vague principles such as achieving a balance budget first. This also implies massive reforms in an educational system that graduates functional illiterates and pushes young people out of school before they've acquired the capabilities of becoming independent earners.

The process of creating jobs is also the process of creating productive, meaningful and creative work - building houses for a nation that cannot meet the housing needs of all of its people, caring for a ravaged environment and creating an infrastructure of services and public facilities that will make our society more humane by helping each person to fulfill his or her potential.

A second major goal should be an income assistance program. The deficiencies of both the present welfare system and the administration's reform plan could be overcome by reliance on a refundable credit income tax consisting of a grant to each person; higher income individuals would have the grant taxed back while low and moderate-income persons would keep all or part of it. Tied to a revamped tax system that eliminates the billions of dollars in loopholes and tax preferences, such a system would no longer stigmatize the poor; it would provide assistance for lower-income families not now eligible for welfare payments. The result would be a more equitable tax system.

The administration's current welfare reform plan is an improvement over the present system and may well be the most feasible politically possible measure at this time. But it should not be seen as an end in itself. Rather, it should be a beginning toward a comprehensive income assistance program that fundamentally alters our conception of "welfare."

A third policy goal should be revitalization of the cities through a national urban policy supportive of urban growth and economic development. A coordinated, systematic approach to urban problems is necessary, and should include urban banks, a national urban economic development bank, sharply expanded housing opportunities for low-income families, transportation programs and educational aid.

Other major reforms high on the agenda include a national health policy that not only cushions families against rising medical costs but also assures equal access to quality medical care and removes income as a determinant of health.

THE VERY length and extent of the "shopping list" of new policy initiatives is a measure of the nation's needs. And, while I have outlined the most pressing items on black people's agenda, it should be clear to all that more whites than blacks would benefit from them. The great majority of people without jobs are white, the majority of those on welfare are white, and the majority of America's poor people are white.

But it should be equally clear that, while measures intended to benefit all Americans are implemented, special steps must be taken to ensure that black people come to enjoy parity with whites. It is not enough simply to pursue aggregate policies that increase the number of jobs or homes, for example, without targeting those policies to ensure that blacks and other disadvantaged minorities get their fair share of those jobs and homes.

Alongside such basic policy steps, the President and his administration could make those symbolic gestures that are vital ingredients of national leadership. In his actions and rhetoric, the President can demonstrate his concern for America's poor and her minorities. The symbolic acts of his first days in office signaled to the nation the new administration's openness and its more populist style. So, too, can the President send signals to the urban poor.

One such signal, costing no more than the fuel for Air Force One, would be to visit deprived urban neighborhoods. A President who went to Clinton, Mass., and Yazoo City, Miss., should also walk the mean streets of the South Bronx or Brooklyn's Bushwick section to assure people of his concern and of his determination to help them change their lives.

Another signal should be to order his Justice Department to file a brief in the Bakke case, coming before the Supreme Court this fall, supporting the University of California position that it legitimately reserved 16 of the 100 seats at its Davis medical school for it minority students and that this did not violate Alan Bakke's constitutional rights.

By making his concern for the poor apparent, by taking every opportunity to demonstrate that he cares and that his administration will fight to change conditions that keep people chained to poverty and despair, the President can not only rekindle the embers of hope in our cities, but he can help lead the majority of Americans out of their indifference and toward greater social concern. The anti-social selfishness that characterized the nation in the past decade is as harmful to the future of American democracy as is the bleak anti-social despair fostered by urban poverty.

So long as this administration clings to caution and to priorities that are at odds with its campaign promises and the expectations of activism they engendered, it will suffer a credibility gap of increasing dimensions and will be further estranged from its natural constituency. More important, a magnificent opportunity will have been missed to change millions of lives for the better, and that failure may mean deepened despair and cynicism among America's poor.