Washington — In calling this week for a grant of limited immunity for two former White House aides involved in the Iran-contra affair, President Reagan says he wants a full disclosure of the facts about secret National Security Council operations. But some members of Congress and legal experts are concerned that rather than spark a full disclosure of the facts, limited immunity may only make it more difficult for prosecutors in the weeks ahead to build sound cases against two of the reported key officials involved in the broadening scandal. They suggest that it is too early to discuss possible grants of immunity for the former national-security adviser, Vice-Adm. John M. Poindexter, and a former NSC staff member, Lt. Col. Oliver L. North.
``The American people are entitled to a full and accurate account of the truth; they are also entitled to have justice done,'' says Archibald Cox, the former Watergate special prosecutor, who urged Congress to reject the President's request.
Mr. Cox adds that Americans ``are more likely to have justice done and receive the whole truth after deliberate investigation than by hurried revelations under promises of immunity.''
Senate leaders, members of the Senate Intelligence Committee, and a majority of the newly appointed members of the Watergate-style special Senate committee to investigate the Iran-contra affair say it is premature to consider possible grants of limited immunity to Colonel North and Admiral Poindexter.
``I have been through these grants of immunity before.... It has to be done very carefully,'' says Sen. Sam Nunn (D) of Georgia, who is one of 11 senators appointed Tuesday to the special Iran-contra investigation committee.
Senator Nunn added, ``You have to be thoroughly prepared so you know you are going to get truthful testimony.''
Under a grant of limited or ``use'' immunity by Congress, prosecutors would be barred from using the congressional testimony of either North or Poindexter to assist in any way in building a criminal case against them.
If limited immunity were granted, prosecutors in the weeks ahead could face legal challenges requiring them to prove that the information uncovered by criminal investigators had not stemmed from leads developed from North's or Poindexter's congressional testimony.
Several senators have said that grants of limited immunity should not be considered until after the special prosecutor has concluded his inquiry into potential criminal wrongdoing. The special prosecutor has not yet been named. And the senators stress that the members of the Senate select committee were only named this week and will not get down to the business of launching a comprehensive probe until the new Congress begins its session in January. A similar House committee has not yet been named.
The Reagan administration has an interest in resolving the Iran-contra affair quickly. Public opinion polls show that news of the secret Iran arms deals and efforts to divert profits to the Nicaraguan contras has done serious damage to the President's popularity.
``We want to get to the bottom of this, and we want to do it as quickly as possible,'' says White House spokesman Larry Speakes.
Some members of Congress suggest that the President's call for a grant of immunity is an indication of the administration's failure to live up to its earlier pledge that it would facilitate full cooperation in probes of the Iran-contra affair.
Others, however, see the President's request as a means to put the Iran-contra scandal behind the administration so that it can get on with more pressing issues.
``Limited use immunity would provide the missing pieces of the puzzle,'' says Sen. Orrin Hatch (R) of Utah. ``It would be beneficial to the presidency, to our foreign policy objectives, and to our national-security interests.''
Senator Hatch, also a member of the special Iran-contra committee, suggests that limited immunity should be granted not only to North and Poindexter, but also to retired Air Force Maj. Gen. Richard V. Secord, who has been identified as a key associate of North, and two other unidentified persons.
``I think it is important to get to the bottom of this by letting those people testify and by letting the American people know what happened,'' Hatch says.
Most of Hatch's Senate colleagues disagree. ``It is just too early to know enough facts about who did what,'' says Howell Heflin (D) of Alabama, a former chief justice of the Alabama Supreme Court and a member of the select committee. ``I think you have to have a lot more facts and you have got to evaluate those facts before you can consider immunity,'' Senator Heflin says.
White House spokesman Speakes said yesterday that President Reagan was ``disappointed'' that lawmakers appeared opposed to his request and hoped they would continue to consider it. Speakes added that the President has not ruled out using his power to grant executive clemency, or a pardon, to protect his aides from incriminating themselves, but that Reagan plans no such action now.