THE last few years have seen a welcome drop-off in random terrorism - the plane bombings, ship hijackings, and airport attacks done for political reasons but against arbitrarily selected victims. Whether for reasons of tightened security or changes in political strategy by terrorists and their sponsors, such violent actions to seize the world's attention and publicize grievances are not as fashionable as in the mid-'80s.Sadly, however, in some quarters murder has not been shelved as a political tool. Among those most willing to kill for politics today are extremists alarmed at the prospect of peace. This strain of extremism may have been behind the assassination last week in Paris of Shahpur Bakhtiar, the last prime minister of Iran under the shah. Since his exile in 1979 after the Islamic revolution, Mr. Bakhtiar has been a critic of Iran's mullah regimes. On Sunday, however, the Tehran Times, a newspaper that usually reflects the thinking of Iranian President Hashemi Rafsanjani, criticized the killing as an effort to block the improvement of relations between Iran and France. Radical Iranian dissidents are opposed to any opening to the West by the Rafsanjani government, widely seen as more moderate than the Khomeini regime. Bakhtiar's murder furthermore appeared to have been intended to raise tensions and abort the wider peace process in the region as well as the release of hostages. Within the Palestinian community, certainly, the assassin's bullet and blade are wielded against would-be peacemakers. In the occupied territories this year, Palestinian deaths at the hands of other Palestinians for political reasons exceed those caused by Israeli security forces. Now death threats have been issued against any Palestinians who agree to sit down with Israel at an international peace conference. The intended victim, of course, is the peace process itself. Throughout the Middle East, there is hopeful movement toward resolving heretofore intractable problems. These developments must not be blighted by a handful of remorseless killers. It is a time for courage and resolute defiance of the assassins of peace.