THE motion by Lawrence Walsh, the special prosecutor in the Iran-contra affair, to drop the main charges against Oliver North leaves frustration in its wake. Many suspect that the full truth of Iran-contra - including the roles of President Reagan and President-elect Bush - remains cloaked in secrecy. Walsh's decision means, however, that there likely will be no further probing of the central facts in a rigorous criminal trial. (North still may be tried on lesser charges.)
The dissatisfaction is compounded by the fact that Walsh's motion to drop the charges of theft and conspiracy to defraud the government came as a result of a ``technicality:'' some key evidence is contained in sensitive intelligence documents that cannot be made public.
But in an imperfect world there is not a legal remedy for every wrong. In this case, society's strong interest in justice smacks up against the nation's equally imperative interest in security. It's a mark of a mature polity that it can accept such unpalatable tradeoffs.
Some doubters see self-preservation more than national security behind the government's decision to protect classified documents. But Walsh himself has refused to impugn the government's motives.
Walsh's motion has renewed attacks on the office of ``independent counsel,'' which was created by Congress after Watergate. Critics point to the high cost of Walsh's investigations - more than $13 million to date, even before the trials of North and three other defendants. They also say it is unfair to appoint a prosecutor with unlimited staff and budget to ``go after'' a single defendant, a prosecutor free of many of the constraints on ordinary district attorneys.
To be sure, the system has potential for abuse. The recent two-year, futile investigation of Theodore Olson, a former Justice Department official, gave off a whiff of prosecutorial excess.
Despite such risks, there are occasions when the government cannot be allowed to investigate itself - either because actual impropriety may taint the investigation, or because perceptions of impropriety may undermine public confidence in the justice system.
It would be hard to imagine a case that cried out for a special prosecutor more than the Iran-contra affair - which involves major legal and ethical issues, and in which the conduct of some Justice Department officials has been called into question. Far from discrediting the office, Walsh's investigation - tough, dogged, but fair - has confirmed its usefulness. For public confidence in the integrity of our legal system, even $13 million is a small price to pay.