An appeals court yesterday threw out the 1972 conspiracy and arson convictions of the "Wilmington 10," the North Carolina civil rights workers whose imprisonment prompted an international controversy about American justice.

A three-judge panel of the 4th U.S. Circuit of Appeals ruled that there were critical unanswered questions about the credibility of key prosecution witnesses. Some received special favors from prosecutors in the case and one, the most curcial witness, provided two versions of the crime on two occasions.

"The conclusion is inescapable," the appellate panel said yesterday, that the prosecution's most crucial witness, Allen Hall, "prejured himself in his testimony . . . and this fact was bound to be known to the prosecutor."

These flaws led Amnesty International to declare the Wilmington 10 America's "political prisoners" and prompted the Justice Department in 1978 to intervene for a reversal of the convinctions and drew a "friend of the court" brief from 55 members of Congress.

The civil rights workers, led by Ben Chavis, field organizer for the United Church of Christ, nevertheless served as much as four years in prison before the last was paroled.

Chavis yesterday expressed joy at the appeals court decision, but his elation was mixed with regret. "We should have never been convicted. We were totally innocent of those frame-up charges and had to sufer many years unjustly."

Another defendant, Joe Wright, 28,, said he was "jumping for joy."

The racial controversy that became the Wilmington 10 case began in late 1970, when black students at the high school in that North Carolina town charged they were being discriminated against. Chavis went to Wilmington at the request of a black minister in January 1971.

The next month, violence broke out and two persons, one black and one white, were killed. White-owned Mike's Grocery was burned and Hall was soon charged with arson. He later turned state's evidence, and implicated Chavis, eight other black men and a white woman. After one mistrial, all 10 defendants were convicted and sentenced to long jail terms.

The appeals juges, in an opinion written by Harrison L. Winter, with John D. Butzner and James M. Sprouse, said that Hall's testimony differed in 15 different respects from a statement he had earlier given the prosecutors. Yet the prosecutor and the presiding judge refused to let the jury see the statement, and thus be made aware of the contradictions.

The court also cited special treatment given Hall and another witness, Jerome Mitchell. They were allowed to stay at hotels and in a beach house, instead of in a jail. They were allowed a visit to their homes. Hall got a visit from his teen-aged girlfriend. "Above all," the court said, Hall assaulted deputies during his stay in custody and was not punished for the attack.

"All of that was withheld from the jury," the court said, yet it "spoke directly to the credibility of the witnesses."

Also withheld from the jury and the defense lawyers was the fact that Hall, in the court's words, was a "borderline defective." This knowledge might have suggested to jurors that "he lacked the ability to recall accurately events about which he testified with such exquisite detail, that had occurred at least one and a half years prior to the time he was to testify."

The Wilmington 10 are now innocent of the charges against them. The charges still stand, however, pending a decision by North Carolina prosecutors about whether to retry them or appeal yesterday's ruling to the U.S. Supreme Court. Officials had no comment yesterday on their plans.