Iran-Contra prosecutors are using a new grand jury to review testimony from last year's congressional hearings in an apparent investigation of possible perjury by witnesses in the case.

The prosecutors working for independent counsel Lawrence E. Walsh have been playing videotapes of the House-Senate hearings to the federal grand jury that has been meeting regularly on the case for about three weeks, said sources who spoke on condition of anonymity.Because grand jury proceedings are secret, it is unclear who might be suspected of lying under oath, either to Congress or to the original Iran-Contra grand jury that returned indictments earlier this year.

But the panel could compare testimony a witness gave to Congress with facts developed by Walsh's investigation, as well as sworn statements that the individual or others made to the original Iran-Contra grand jury.

So far, the grand jury has not heard any live witnesses, according to the sources, indicating prosecutors are laying groundwork for the investigation by playing the videotapes of the 1987 hearings.

The grand jury has been meeting two or three times a week for several hours. It hears other cases unrelated to the Iran-Contra affair.

The new grand jury, unlike the one that indicted former White House aide Oliver L. North and other figures in the Iran-Contra affair, is free to review congressional testimony given under grants of limited immunity from prosecution for evidence of perjury.

Such grants of "use immunity" prohibit prosecutors from using a witness' testimony or evidence derived from it to prosecute that individual in court on criminal charges.

The immunized testimony, however, could be used as evidence in a perjury case if the witness lied to Congress or a grand jury.

It could also be used as evidence that another person committed a crime, raising the possibility the new panel could develop leads from the congressional hearings that could not be followed up by the original Iran-Contra grand jury.

Walsh and most of his prosecutors carefully isolated themselves from news coverage of the House-Senate committee hearings to avoid exposure to the immunized congressional testimony.

The independent counsel did not want to be left open to defense accusations that his office illegally relied on the immunized testimony as evidence to prosecute the Iran-Contra defendants.

He also took measures to ensure that members of the original Iran-Contra grand jury were not exposed to immunized congressional testimony.

The team of prosecutors presenting evidence to the new grand jury is led by K. Chris Todd, one of the few members of Walsh's staff who has been exposed to the congressional testimony.

Todd's appearance at the proceedings signaled that the new Iran-Contra grand jury is reviewing immunized congressional testimony and that perjury is a likely subject of the inquiry.

Walsh said in court last spring that Todd had been exposed to testimony given to Congress and was not participating in the prosecution of North, former national security adviser John M. Poindexter and arms dealers Albert Hakim and Richard V. Secord.

But Walsh testified that Todd was continuing to do unspecified work on his staff.

North, Poindexter, Hakim testified on Capitol Hill under limited grants of immunity from prosecution. They are accused of conspiring to defraud the government by diverting millions of dollars of proceeds from the U.S.-Iran arms sales to the Nicaraguan rebels.