The Justice Department is making a third attempt to censor evidence in the Iran-Contra trial of Oliver North, after being told twice by the courts that it has no business interfering in the case.

The department wants a three-member panel of the U.S. Court of Appeals to reconsider its decision Thursday lifting an administrative stay that had blocked North's trial from proceeding. The department said that it would return to the appeals court this morning.At issue is whether national security would be threatened by disclosure of classified information during North's trial. The Justice Department, at the urging of the CIA and National Security Agency, is seeking authority to screen and block such disclosures.

U.S. District Judge Gerhard Gesell, who is presiding at the trial, has ruled that North may use classified information if it is relevant to his defense against charges of covering up the Iran-Contra affair.

Gesell finished selecting a jury on Thursday and he rejected the Justice Department's censorship bid, calling it "wholly misplaced." He told the jurors to report back Monday morning.

Gesell said the Justice Department has no standing to interfere in the trial at this point because Independent Counsel Lawrence Walsh is handling the prosecution of North.

A few hours later, the appeals court upheld Gesell's decision.

Loye Miller, a Justice Department spokesman, said it would try again today because on Thursday the appeals judges "had before them a lot more" material from Walsh "than they had from us."

Assistant Attorney General Edward S.G. Dennis, head of the Justice Department's criminal division, claimed that "the risk to national security would be significant" under the rules laid down by Gesell. He said the government would lack control over "disclosure of very sensitive, classified information."

Gesell issued a ruling Jan. 19 permitting North to introduce classified material if it tends to show that North's purpose was not to violate the law, or that government witnesses are lying.

He also said North may use classified information, where relevant, about the Reagan administration's efforts to have other countries aid the Nicaraguan Contra rebels after Congress had banned U.S. military aid.

North is charged with concealing from Congress and the attorney general the administration's secret support for the Contras during the period in which direct U.S. aid was banned.

North also is accused of illegally accepting installation of a security system at his home, converting to his own use at least $4,300 in traveler's checks from a Contra leader, and conspiring to use a tax-exempt foundation illegally to raise money for the rebels.