A federal appeals court Tuesday refused to reconsider its decision setting aside Oliver L. North's Iran-Contra convictions.

The U.S. Circuit Court of Appeals here denied a petition by independent counsel Lawrence E. Walsh that the 12-member court rehear the case decided in July by a three-judge panel.The court's refusal to rehear the case means that U.S. District Judge Gerhard A. Gesell must hold a hearing to determine if the 1987 testimony North gave Congress under a limited grant of immunity from pros-ecution had unfairly seeped into the trial.

But independent counsel Lawrence E. Walsh could appeal today's decision to the Supreme Court, an action that would delay the hearing.

In its July 20 decision, the three-judge panel set aside the three convictions pending such a hearing by Gesell.

North was convicted of helping to prepare a false chronology of the Iran-Contra affair for Congress, altering or destroying National Security Council documents and accepting an illegal gratuity - the installation of a security fence outside his home.

The retired Marine lieutenant colonel and former National Security Council aide was placed on probation and ordered to perform community service.