President Reagan is enormously popular at this point with every group of American voters except blacks, and an analysis of Reagan's proposed budget cuts suggests one reason why: some of the biggest cuts would come in programs vital to blacks.

Medicaid, publicly assisted housing, food stamps and other benefit programs Reagan wants reduced serve a much larger proportion of the black population than of the white.

On the other hand, the so-called safety-net programs, such as the Social Security, Medicare and veterans' benefits, which Reagan has pledged not to cut, are programs that benefit the population proportionally, which means they benefit whites overwhelmingly.

Stereotypes to the contrary, there are in absolute numbers more whites than blacks in most of the basic multibillion-dollar federal benefit programs, including welfare.

But the test is not what percentage of a program's beneficiaries are black, it is what percentage of blacks in the country depend on a program. And by this test the impact of the Reagan cuts on minority groups is likely to be severe.

In the food-stamp program, for example, Uncle Sam helps pay the grocery bills for about 8 million families. Nearly three of every five are white, according to a survey by the Agriculture Department about a year ago.

But it is also true that roughly one of every three black families in America uses food stamps. About seven of every 100 white families in the continental United States receive food stamps, compared with 36 of every 100 black families.

Reagan proposes saving $1.8 billion next budget year by striking about 400,000 families from the food-stamp rolls by cutting off households with annual incomes of $11,000 or more. Currently, a family of four with annual earnings up to $14,000 is eligible for food stamps.

As with food stamps, so with Medicaid, health care for the poor, which pays the doctor bills for nearly one of every four minority-group members in the country.

Medicaid serves 22 million Americans, about 10 million of them minority members. Reagan proposes to shave $1 billion off the federal contribution to this $18.2 billion federal-state program and give states greater control over it than they have now.

The $3.5 billion in cuts Reagan has proposed for Comprehensive Employment and Training Act (CETA) public jobs program would mean the loss of about 100,000 jobs held by blacks.

That reduction in federally subsidized jobs is nearly enough to raise the already high national unemployment rate for blacks up by a full percentage point. Last month, 13.9 percent of blacks in the labor force were out of work, compared with 6.7 percent of whites.

The federal government provides shelter or helps pay the rent for about one in every five minority-group families. Federal housing subsidies for the poor represent one major social program in which racial minorities do form the majority of beneficiaries.

Reagan intends to cut back President Carter's proposed expansion of rent-assistance programs, though he too would expand them, and increase the rents required from needy families. The president also wants to postpone funds for major repairs and maintenance on public housing projects, home for more than 600,000 families from minority groups.

The $5.2 billion government-aid program for needy college students has been considered generally responsible for the dramatic rise over the last decade in the numbers of black youths going to college.

Reagan has proposed limiting aid to poorer students to cut budget outlays of $5.2 billion by a sixth at first and more later, though it is not clear that this reduction would hurt black students more than white students, because the cuts would affect upper-income families more.

About 2.6 million college students will receive grants this year. About one of every three students who received aid when the program was surveyed two years ago were black.

Two of the sacred cows are programs with a majority of black recipients, Head Start and the summer youth jobs program. But, unlike the others on the list of untouchables, annual appropriations for each of these are relatively small, slightly less than $1 billion.

Head Start for preschool youngsters is popular among educators. The summer jobs program for urban youth has been regarded cynically in previous administrations as "riot insurance."

The president's proposal for reducing taxes would also not be a boon to most blacks, since minority families' income still lags considerably behind that of white families and the Reagan tax cuts promise the greatest benefit for upper-income brackets.

Census statisticians found two years ago, for instance, that about three of every five black families had earnings of less than $15,000 a year, incomes for which the maximum tax cut for a family of four under the president's proposals is expected to be about $75 this year and $185 next year. Fewer than 6 percent of all black families earn more than $35,000 annually, the brackets where there would be the biggest dollar tax reductions.

Benjamin Hooks, executive director of the NAACP, speaking for his and other civil rights organizations, said this week that they will fight the proposed cuts "with every fiber of our being and every resource at our command."

"Whatever the odds, we will resist and not bow," Hooks said. "We will employ litigation when our constitutional rights are in jeopardy, engage in the drama of mass demonstrations to educate the American people, engage in political action and voter registration and use the tactic of economic withdrawal."

But privately, some black leaders exhibit alarm and real bewilderment about the best strategy for stopping the cuts from going through. They are looking for allies to go against a very popular president whose plans for economic recovery have so far earned him broad support.

What Hooks and others must come to grips with are the radically differing perceptions of blacks and whites about both the president and his economic recovery program.

Whites, who appear to be less affected by the cuts, seem to take Reagan at face value when he says the truly needy will not be hurt, according to the results of an opinion survey conducted by The Washington Post and ABC News.

But blacks neither go along with the economic program nor regard the new president with much esteem, according to the Post-ABC poll. Blacks tend to view Reagan as the rich man's president, while most whites believe he wants to serve all equally. Most whites do not believe the budget cuts will hurt government programs or the poor.Most blacks do, according to the poll.

These differences in views extend to the question of how the nation got into the morass of inflation and high unemployment in the first place.

Whites tend to believe, as Reagan says he does, that it is the fault of big government. Blacks say they feel on the whole that the soaring price of oil has caused the problems, and that they have little faith that budget cuts will help curb inflation.

While blacks find themselves in opposition to a new president and to his policies, they are still hopeful about the future. When asked by the poll about their expectations, blacks were optimistic, even more confident about an improved future than whites were.