The May 17 Miami riot was no accidental hot summer incident but a direct reaction to a feeling that justice for blacks does not come out of a white system.

Pollster Robert Ladner, executive director of the Behavioral Science Research Institute, came to this conclusion after surveying 444 blacks in Miami and surrounding Dade County in a poll commissioned by The Miami Herald and financed, in part, by The Washington Post.

The survey revealed unprecedented levels of frustration and bitterness, in comparison with a similar poll conducted in 1968.

The new poll found:

Seven out of 10 blacks surveyed listed "the McDuffie incident" as the major cause of the rioting five weeks ago, followed by "injustice." In the "MdDuffie incident" an all-white jury acquitted four white ex-policemen of the fatal beating of black insurance executive Arthur McDuffie.

More than 26 percent of the riot area residents surveyed said they participated in the disturbance. That's almost twice the percentage of persons who acknowledged joining in the major race riots of the 1960s.

Riot participants were almost indistinguishable from nonrioters in Dade County (Miami). Three out of every four said the Dade state attorney's office is "biased" against blacks.

Blacks say whites exert too much control over the black community. Four out of five say there aren't enough black leaders in Dade County. Nine out of 10 say a white man "can get away with anything."

Almost nine of 10 blacks say the newly arriving Cuban refugees will hurt their chances for progress. Blacks deeply resent what they say is the disproportionate ease with which Cuban immigrants have advanced up the social and economic ladder. But only 4 percent of those surveyed listed the Cuban influx as one of the four major causes of the rioting.

"One of the most compelling findings in these data is that the riots were based on a cause that the rioters -- and a great many nonrioters -- thought was just," Ladner said.

To determine black attitudes, the Herald pollsters questioned a randomly selected sample of blacks between June 2 and 11 in areas where the heaviest riot-related violence occurred.

Respondents were asked more than 150 questions by black interviewers. Persons were questioned in their homes and apartments, in restaurants, bars and on street corners. Black homeowners, renters, transients and teen-agers participated in the poll. The error margin of the survey is less than 5 percent.

To determine historical changes in community attitudes, the questionnaire duplicated more than three dozen questions asked in a 1968 Herald survey of local black attitudes.

A comparison of results disclosed that the black community feels its problems are more serious now than they were 12 years ago.

An example, 23 percent of blacks surveryed in 1968 rated police brutality as a "big problem" in their neighborhood. Today nine out of 10 blacks believe police brutality is a major problem. The poll also showed that the rioting last month, which left 17 dead and more than $50 million in property damage, was not a product of the long, hot summer syndrome believed responsible for most major racial disturbances of the 1960s.

Instead, it was an explosion of emotion against specific instances of perceived injustices -- a swift and deadly reaction to a political, judicial and economic establishment that, in the words of one 29-year-old rioter, "had gone too goddamn far once too often."

The specific causes of the riot: A succession of court cases that confirmed in the minds of blacks that justice in Dade County is color-coded. The poll showed that those perceived wrongs, set against long-standing problems of unemployment, poor housing and inadequate schools, provided fuel for an explosion in the black community.

The riot catalyst was the McDuffie verdict. More than 70 percent of blacks surveyed said the McDuffie incident was the single greatest cause of the rioting.

But the blacks surveyed said McDuffie wasn't the only reason for the unrest.

Almost two out of five listed "the unfair judicial system," as the second greatest cause of the rioting.

The third leading reason for the riots, listed by 28 percent of the respondents, was the trial and conviction of former Dade County school superintendent Johnny Jones.

Jones was found guilty April 30 by an all-white jury of attempting to use school funds to buy luxury plumbing fixtures for his Naples vacation home.Seventeen days later, another all-white jury acquitted four police officers accused of killing McDuffie.

It is a measure of black anger with the criminal justice system -- and proof of Jones' stature in the black community -- that the former school administrator was rated in the poll as the second most effective black leader in Dade County.

"The police killed a man and were set free," said a 72-year-old man interviewed by the Herald. "Johnny Jones didn't kill anyone and was convicted."