IRAQI President Saddam Hussein is once again engaged in brinkmanship with the United Nations. UN weapons inspectors have been prevented from installing surveillance cameras at two missile testing sites, in defiance of the terms of the Gulf War cease-fire. The move has renewed fears he is trying to build new weapons of mass destruction or medium-range missiles. Saddam's acts of defiance do nothing for his own people. The country may face renewed military attacks from the UN. More immediately, it is unlikely to win early UN approval for the sale of oil over six months to pay for food and humanitarian supplies, since the sale depends in part on its compliance with last month's Security Council resolution demanding that it allow the cameras to be installed. Human nature and the Iraqi propaganda machine being what they are, however, Saddam probably assumes that whatever privations the UN inflicts on his country in punishment will do his personal standing with the Iraqi people a power of good. It will give him a new propaganda weapon and divert domestic attention from the continued waste of his nation's resources on megalomaniac weapons development. Yet if the present battle with the UN ends in a stand-off, he will take even greater liberties in future. Saddam has nothing to lose by such arrogance. It is a tragedy the same cannot be said for the Iraqi people. But what would he care?