Former White House aide Oliver L. North made his fourth appearance yesterday before a grand jury that is continuing to investigate the Iran-contra affair.

The retired Marine lieutenant colonel, who served as a National Security Council staff officer during the Reagan administration, testified behind closed doors at the federal courthouse.

The grand jury, which was impaneled in May, is being used by independent counsel Lawrence E. Walsh to determine if other Reagan administration officials participated in efforts to deceive Congress about the sale of U.S. arms to Iran and the covert military assistance to the Nicaraguan contras, sources say.

North, who is appealing three Iran-contra convictions, was accompanied by defense attorneys who waited in the hallway outside the grand jury room while his testimony was in progress.

The former White House aide, who coordinated a secret arms resupply operation after Congress had shut off such U.S. aid to the rebels who opposed Nicaragua's Sandinista government, testified three times last month.

The grand jury also has heard testimony from North's former boss, John M. Poindexter, the Reagan administration national security adviser who was sentenced last month to six months in prison for lying to Congress about the Iran-contra affair.

Poindexter, who is appealing his conviction, spent nearly six hours testifying before the grand jury last month and is expected to be called back before the panel for more questioning.

The grand jury is also performing a final assessment of the roles of then-President Reagan and then-Vice President Bush in the Iran-contra affair.