WHEN the Iranian government sent a mob to invade the United States Embassy and then held diplomats prisoners for 14 months, there was justifiable outrage in the US over this breach of the international legal principles of diplomatic immunity and the inviolability of diplomatic property.
Now more than a dozen prominent leaders, including members of Congress, have deliberately gotten themselves arrested for violating the South African Embassy in Washington in protest against South African treatment of blacks in general and of 13 arrested black labor leaders in particular. The protests were started by the Rev. Walter E. Fauntroy, the District of Columbia's nonvoting delegate in the House of Representatives. Mr. Fauntroy and his associates, including a US civil rights commissioner, Mary Frances Berry, refused to leave the embassy after a meeting with the ambassador. They thereby committed the same breach of international law as the Iranians, albeit on a smaller scale and in a more genteel fashion.
US embassies need the protection afforded by international law more than embassies of most other countries. Yet one reason US protests over Iranian behavior did not elicit a more sympathetic response was the widespread notion that the US itself violates international law when it suits its purpose. An example frequently cited was US covert involvement in the overthrow of Iranian Premier Mohammed Massadegh in 1953. The Reagan administration provided a further example this year when it rejected the World Court jurisdiction over US actions in Nicaragua. Members of Congress have now provided another.
Some have likened the Fauntroy action to the mass civil rights sit-ins of the 1960s which were also illegal, but under local - not international - law. This is perhaps a distinction without a difference, but international law would seem worthy of higher respect. Further, the civil rights movement had to do with America's own problems, not somebody else's.
The members of Congress and their supporters are not only protesting South African policies; they are also, they say, protesting the policies of the administration toward South Africa. US public protests have a better chance of influencing the latter policies than the former.
The Fauntroy group might, for example, have sought an appointment with the secretary of state and then refused to leave his office. This would also have been illegal, and it would have been much more embarrassing to the administration. Would the State Department go so far as to have a member of Congress and an official of another government agency physically ejected from the department's premises? Would it have them arrested?
This course would have had the advantage, from the protesters' point of view, of generating even more publicity than violating the South African Embassy. It might have generated more public pressure on the administration to reconsider its South African policy.
A case can even be made for the Reagan policy of ''constructive engagement'' with that country. We need South African cooperation to settle the long-smoldering problem of Namibia, something which the protesters presumably favor and toward which Reagan diplomacy has produced slow and painful progress.
Still, it is distasteful having close relations with a government like the one in South Africa. It would be more comfortable to distance ourselves from it; but if we do, we ought to recognize that this might impair attainment of our goals in Namibia and possibly elsewhere in Africa.
The members of Congress have legislative means to bring pressure on the Reagan administration, thus indirectly on South Africa. Congress could, for example, refuse to appropriate funds for the US Embassy in South Africa and thereby sever diplomatic relations. Some argue that members of Congress have in fact proposed less extreme measures which did not pass. But the measures Congress proposed to get the US out of Vietnam, or to enact effective civil rights legislation, did not pass initially, either.
Let the congressmen try to persuade a majority of their colleagues in the House to support their view. Let them try to bring public pressure on Congress to do so. But let them not violate diplomatic property. That tarnishes an honorable objective and reduces it to the level of the government it seeks to change. It is acting on the premise that the end justifies the means. Members of Congress ought to behave better.