Former White House aide Oliver L. North testified for about seven hours yesterday before a new federal grand jury that is continuing the Iran-contra investigation, probing issues including whether former Reagan administration officials lied to Congress about the scandal.

North interrupted his testimony at least 15 times to confer with his four-member legal team, led by Brendan V. Sullivan Jr. The lawyers waited outside the grand jury room in a nearby office because defense lawyers cannot appear with their client before a grand jury. However, a witness can interrupt the proceedings to confer with a lawyer.

North's appearance was considered likely to be his most exhaustive questioning yet by Iran-contra prosecutors. Associate independent counsel Craig Gillen, a former federal prosecutor from Atlanta, and other aides to independent counsel Lawrence E. Walsh have spent months preparing for this new phase of the criminal probe that has lasted nearly four years.

Previous questioning of North -- at his trial last year and as a witness in the recent trial of former national security adviser John M. Poindexter -- was confined to the narrow issues in both cases.

Sources have said the new inquiry is expected to focus on whether former Reagan administration officials not previously charged were part of a conspiracy to mislead Congress about secret arms sales to Iran and the arming of the Nicaraguan contras during a two-year congressional ban on U.S. military aid to the rebels.

At one point yesterday, Sullivan, who is known for his fiery defense of North, began shouting at Gillen in the corridor outside the grand jury room. His exact words could not be heard because reporters' access to the grand jury corridor is restricted.

"Let me tell you something," Gillen replied, standing close to Sullivan. "You don't intimidate me, and I don't intimidate you."

Gillen then returned to the grand jury room. North followed a few minutes later.

North was convicted last year of three felonies for his role in the scandal and is presumably appearing before the grand jury under a grant of immunity.

Walsh is expected to focus on former Reagan administration officials' knowledge of North's secret contra work.

Sources have said that among those Walsh would like to investigate further are Donald P. Gregg, who served as national security adviser to then-Vice President Bush and is now U.S. ambassador to South Korea; Elliott Abrams, former assistant secretary for inter-American affairs; and Alan Fiers, a former CIA official.

When the session ended, Gillen told North to return Wednesday. North said nothing as he left the federal courthouse.