Every prosecutor and defense attorney in the country knows of the importance and sometimes the difficulty of securing an unbiased jury in criminal trials. Cases on this topic are always before state and federal appellate courts. Some involve general principles that defendants hope to extend in their favor. Are defendants entitled to be tried by a jury that includes members of their own age group, as a Massachusetts court ruled? In counties where blacks regularly serve on juries, is it unconstitutional for a prosecutor, in a single case, to use his peremptory challenges to exclude all prospective jurors who are of the same race as the defendant?

Other appeals involving challenges to juries do not ask courts to break new ground but simply to review what happened at a specific trial and determine whether a mistrial should have been declared. One of these is the case of Daniel Heller, a Miami attorney who was convicted of tax evasion in 1983. The case was given national attention because the Dade County Bar Association, which ordinarily would suspend an attorney convicted of such a crime, had refused to take that step in Mr. Heller's case because of charges that the jury that convicted him had been tainted by anti-Semitism. Last week, the U.S. Court of Appeals for the Eleventh Circuit reversed his conviction on these grounds and sent the case back for retrial.

The evidence of jury misconduct in the Heller case is compelling. What is astonishing is the trial judge's decision to proceed in the face of these facts. Here was a juror who consulted his neighbor on legal aspects of the case and presented this "expert opinion" to his colleagues during deliberations. Another told racist jokes clearly offensive to the black members of the panel. As for the defendant, right at the beginning of the trial one juror declared, "Well, the fellow we are trying is a Jew. I say, 'Let's hang him.' about the number of Jewish witnesses, jokes about a rabbi who testified and, according to one juror, gales of laughter, in the jury room, over the defendant's plight. The trial judge, after receiving a note from a troubled juror, simply interviewed each member of the panel out of the presence of the prosecutor and the defense attorney -- another mistake -- and asked each to "ignore these extraneous outside matters" and proceed to judgment. Ninety minutes later a guilty verdict was returned.

Mr. Heller's reputation and liberty were at stake. He was sentenced to three years imprisonment after conviction. What was at stake was important, but not apparently to those jurors whose misconduct was brazen and bizarre. A few bad jurors can cause incalculable harm. That's why the task of selecting an honest and unbiased dozen in each case is, and should be, of critical concern to the courts.