In a set of major opinions ending a decade of often bitter wrangling, the U.S. Appeals Court here yesterday shifted the burden to the defendant - rather than the prosecution - to prove allegations that a defendant's attorney hurt his case by the way he handled the trial.

The decision could have wideranging effects on criminal trials and the standards enforced against criminal defense lawyers.

Although the court in its 7-to-2 ruling acknowledged the shortcomings of many members of the defense bar, it refused to specify any criteria by which a defense attorney may be judged. In so doing, the decision set aside previous attempts by then-U.S. Circuit Court Chief Judge David L. Bazelon to set such standards.

In the same case three years ago, Bazelon reversed the conviction of a criminal defendant, Willie DeCoster, on the grounds that DeCoster's court-appointed attorney did not adequately investigate all off his possible trial defenses. However, the full appellate court later set aside that ruling and ordered a hearing before all nine judges.

That hearing occurred more than two years ago, and only yesterday did the full court specify its reasons for reinstating DeCoster's conviction.

The complex set of four opinions, totaling nearly 200 pages, showed no clear agreement on any proper specific standards to apply when a defendant charges that his attorney did not properly represent him. But seven judges ultimately agreed that DeCoster's conviction should be reinstated. Only current Chief Circuit Judge J. Skelly Wright fully supported Bazelon's opinion.

The opinion, written by U.S. Circuit Judge Harold Leventhal for himself and three other judges, said it is up to the defendant to illustrate the likelihood that the attorney's conduct affected the outcome of his trial. After the defendant meets that burden, the government has a chance to show that there was, in fact, no such adverse effect, Leventhal said.

U.S. Circuit Judge George MacKinnon and one other judge went further, saying the defendant had to prove his case actually was hurt by his attorney's conduct. U.S. Circuit Judge Edward A. Tamm went along with both MacKinnon's and Leventhal's opinion.

U.S. Circuit Judge Spottswood Robinson III said he felt the government should be forced to prove the defendant did not suffer harm, and he even said DeCoster's attorney was clearly ineffective. But he agreed with the six other judges that DeCoster's conviction should be reinstated because his attorney's conduct was merely "harmless error."

The only consensus among all nine judges seemed to be that the Constitution requires a defendant to have a "reasonably competent assistance of an attorney acting as the defendant's diligent, conscientious advocate."

"However, a defendant is not entitled to perfection, but to basic fairness," Leventhal wrote, noting that indigent defendants usually suffer the most because of their inability to hire highly paid, topnotch attorneys.

Leventhal and the judges for whom he wrote expressed sympathy with Bazelon's "eloquence" and his "bold but single-valued approach" of setting aside criminal convictions when attorneys do not perform up to certain standards.

Leventhal discussed at length the "real world' of court-appointed defense attorneys who handle high volumes of cases at low pay, and characterized Bazelon's views as aspirations for the legal system.

"We do not think he has made a case for the drastic overhaul of a system that historically has heightened protection of the accused," Leventhal said of Bazelon's position. "Our approach toward the minimum legal obligations of our democratic society to ward off injustice may be more earthbound, but in our view it is more salutary."

MacKinnon, who has been Bazelon's main opponent on the defense standard issue was not as gentle. He said Brazelon's writings on the subject represented a "misguided attempt to change the law," and would force defense attorney's to investigate every possible fabricated defense.

Prosecutors had criticized the earlier Bazelon opinions as, putting an unfair burden on the prosecution to monitor a criminal defense attorney's work. And many defense attorneys had said the Bazelon opinions in effect second-guessed a defense attorney's trial tactics.

DeCoster was arrested on May 29, 1970, in the lobby of a rooming house after a soldier had been robbed of $100 outside the Golden Gate Bar at 8th and K streets NW. The assailants had been chased by the police, who said they had not lost sight of the robbers.

DeCoster, who already has served his sentence of 2-to-8 years, said he knew the victim and had been drinking with him earlier, but he said he did not participate in the robbery.

DeCoster never raised the issue of ineffective assistance of counsel, various appellate judges noted yesterday. Bazelon first brought up the issue himself at an appellate hearing in 1973, and shifted the focus to that issue over the next six-year period.