Defense lawyers who lose criminal cases file motions for a retrial routinely and judges almost as routinely deny them.

Most of the time, motions for a new trial effort by defense attorneys to keep a client out of jail.

But once in a while there is an exception, and such was the case yesterday when millionaire developer Dominic F. Antonelli and D.C. mayoral aide Joseph P. Yeldell won a new trial. Their lawyers showed that a juror had a checking account at Madison National Bank, an institution that Antonelli founded and from which Yeldell received loans endorsed by Antonelli.

The Sixth Amendment to the Constitution guarantees every accused person the right to an "impartial jury," a command that the U.S. Court of Appeals here has translated in a simple way.

"It is the duty of every juror to answer questions affecting his qualifications honestly," the appellate court said in a 1938 decision, "and if he conceals a material fact which, if disclosed would probably have induced counsel to strike him from the jury, a new trial should ordinarily be ordered."

In the Yeldell-Antonelli case, juror Diane P. Jones failed to disclose, when she was asked as a potential juror, that she had had financial dealings with the Madison National Bank.

In a 1966 decision, U.S. Circuit Court Judge David L. Bazelon noted that "neither judge nor counsel can do his part in securing an impartial jury if a juror fails to respond truthfully to questions" put to potential jurors.

Bazelon's opinion said that a "new trial is always required" when it is shown that "the juror was biased against the losing party." Moreover, he said that a new trial must be ordered if a juror's "nondisclosure (of information) resulted from a purposefully incorrect answer or from deliberate concealment." But the appeals court decision said that if the nondisclosure "was innocent the trial court has some discretion in deciding whether to order a new trial."

Although a prospective juror who lies under questioning by a judge or lawyers could theoretically be prosecuted for perjury, such occurences are extraordinarily rare. Prosecutors normally would have to prove to a jury the juror intentionally concealed the information, a difficult proposition at best.

No one knew yesterday how much the Yeldell-Antonelli trial cost the taxpayers, but a considerable amount of money was involved. The 12 jurors in the case and six alternates were sequestered in a District motel and fed by the government during the 17-day trial, an expense that may have totaled $25,000, including the $20-a-dat juror's fee.

In addition, there were 41 withnesses at the trial, each of whom was paid the standard $20 a day. But the same witnesses will $30 a day a new trial under a law recently passed by Congress. Thousands of pages of transcripts cost the government several thousand dollars more.

The government also pays the salaries of the prosecutors. Assistant U.S. Attorney Richard L. Beizer has worked on the Yeldell-Antonelli case now for nearly two years, while Assistant U.S. Attorneys Henry F. Schuelke III and Michael L. Lehr have worked on the case for about eight months. They are each paid an average of $35,000 annually, for a total so far of about $115,000 in wages for the prosecutors.