THE INTERNATIONAL Committee of the Red Cross has broken its customary quiet with a sharp assault on Iran's treatment of its 50,000 Iraqi prisoners of war. Contending that Iran has been violating the Geneva Convention, the Swiss-run organization says the Tehran regime has put at risk the "physical and mental survival" of thousands of Iraqi prisoners taken in the four-year- old Gulf War. It appeals to all states that have signed the convention, and which thereby accepted an interest and obligation to ensure its integrity, to put pressure on Iran to respect it.

In weighing such an appeal, it helps to know that the ICRC has an unparalleled tradition of soberness and discretion. It gains access to prisoners only on a pledge to confine its reports to the governments holding them. It leaves to others he function of aiding the victims of war by drawing publicity to their plight. In now going public about Iran's policy, the ICRC knows full well it is threatening its access to a large group of exposed prisoners whose principal hope of avoiding the full brunt of Iranian arbitrariness has lain, up to this point, in its visits. The presumption must be that the organization took this extremely rare step only because it saw no other way to fulfill its responsibilities to the prisoners held in Iran.

It is necessary to say that Iraq and Iran, under their present regimes at least, are among the last places on earth where one would want to be taken prisoner. The Iranian government is fully entitled to be concerned for the fate of its men -- and, considering the age of some Iranian soldiers, its children -- in Iraqi hands. The present dispute, however, concerns Iraqi prisoners. Iran has seen them as a pool from which to draw recruits for a Shia "liberation movement" to turn back upon Iraq -- impermissibleunder the Geneva code, but done nonetheless. This was the evident context in which a disturbance of some sort took place in an Iranian prison camp last month while ICRC delegates happened to be on the scene. Under their eyes, a number of prisoners were shot down. This disturbance exacerbated the always tense relations between the revolutionary Khomeini regime and the Red Cross, and led to the present impasse.

The regime's secrecy and the ICRC's discretion make it difficult to know exactly what went on in that POW camp at Gorgan last month, and since. That puts outsiders in the position of making a tentative judgment on the basis of the reputation and credibility of the two parties. In this contest, the Red Cross has all the advantages. Ayatollah Khomeini insists on making his own rules, for prisoners as for just about everything else. The Red Cross has an unmatched record of administering fairly the international rules on a matter of the most acute moral and humanitarian consequences. We will know that the latest threat to Iraqi prisoners has been lifted when, and only when, Iran permits the Red Cross to resume, quietly, its vital work.