As preliminary probe of `contragate' ends, phase 2 is set to begin. Congress has learned much, but gaps remain for select panels, prosecutor

Phase one of the Iran-contra probe is coming to an end. Two of the three congressional committees investigating the affair have closed up shop, and it is unlikely that the third committee will unearth major new facts before Christmas. At least one key member of Congress feels the committees have learned most of what there is to know. ``After you tell it once, it has just about been told,'' says Sen. Richard G. Lugar (R) of Indiana, talking about the story of covert United States efforts to sell arms to Iran to secure the release of American hostages and to use the profits from the arms sales to assist Nicaraguan rebels. There may be ``interesting aspects'' yet to be revealed, ``but the story is already an old story,'' he says.

``That's just the impression Republicans want conveyed now that the preliminary hearings are winding down,'' demurs one Democratic Senate aide. ``But there's no way to know for sure. The [Senate] Watergate hearings were [two] months old before news of [President Nixon's secret White House] tapes became public,'' this aide says. He adds that other revelations could be in store as two select congressional committees and a new independent counsel take up the investigation in the coming months.

Last week the Senate Intelligence Committee wrapped up three weeks of closed-door hearings, drawing on testimony from key Reagan administration officials. The House Foreign Affairs Committee also held hearings on the affair.

The House Intelligence Committee has called retired Air Force Maj. Gen. Richard V. Secord for testimony this week. General Secord has been implicated in arms shipments both to Iran and to the contras. However, in an earlier appearance before the Senate panel, Secord refused to testify, invoking his Fifth Amendment right against self-incrimination.

The congressional inquiries have provided investigators with a more detailed outline of the scheme to transfer profits from the Iranian arms sales through Swiss bank accounts to the Nicaraguan contras.

But conflicting testimony over President Reagan's role in the affair plus the decision of the two key witnesses, former national-security adviser John Poindexter and former National Security Council staff member Oliver North, to invoke the Fifth Amendment have left numerous questions unanswered.

The principal blanks in the record are: how much money was diverted to the contras, and what actually happened to it; and when President Reagan authorized the arms sales to Iran.

On the latter question, the congressional panels have heard conflicting testimony. Attorney General Edwin Meese III and White House chief of staff Donald Regan testified that the President learned of the initial arms shipment in September 1985 after it occurred, while former national-security adviser Robert McFarlane says that he instructed Israel to deliver American-made weapons and parts to Iran with Reagan's prior approval.

Next year the congressional investigation into the Iran-contra affair will be spearheaded by special Senate and House committees. The panels will draw on the record already compiled by the three congressional committees.

Meanwhile, a three-judge panel Friday named Lawrence E. Walsh, a former prosecutor, federal judge, and president of the American Bar Association, as independent counsel to investigate the Iran-contra affair. Under the court's mandate, Mr. Walsh has authority to broaden his inquiry beyond the Iranian arms sales and diversion of funds to the contras. He is authorized, for instance, to investigate all aspects of administration support for the contras since 1984, when Congress banned US government agencies from aiding the Nicaraguan rebels.

Also, a separate three-man commission headed by former US senator John Tower will be looking into whether the National Security Council overstepped its authority through its direct participation in the Iran-contra connection. The NSC was established to oversee the formation and implementation of US foreign policy.