ARCS OF CRISIS, fighting in the Western Sahara, Russian troops in Afghanistan -- all of sudden the usual Mideast fare of the Arab-Israeli conflict seems comforting in its simplicity, if only because the players are known and well established.

Now western governments lurch from crisis to crisis confused by updated versions of conflicts made romantic by Beau Geste desert forts, of Kipling's fascination with the Great Game pitting Imperial Britain against the encroaching Russian Bear.

No longer is it just protecting the lifelines of empire which seems to connect crises. Even geopolitics fails to explain Morocco's desert war in the Sahara, the Soviet-backed Ethiopians' inability to smash the equally Marxist Eritreans in the Horn of Africa, the shock waves throughout the Arab oil countries provoked by Iran's call for Islamic revolution.

What common threads do exist are of little comfort to those long content to ignore the intricacies of the Third World and anxious for easy answers. If anything, the problems do stem from the breakdown of the colonial order long imposed by Europe or the Ottomans and the industrialized world's dependence on oil imported from countries eager to destabilize neighbors in an apprenticeship of power.

Ironies abound.

Israel loses valued long-term allies in imperial Ethiopia and imperial Iran. But there are dividends, if only because Israel is never more secure than when Washington and Moscow are spitting at each other.

The loss of Iranian oil and a quarter-billion-dollar market for Israeli goods is balanced in part by the worry caused in arch-enemy Arab states by the shia-sunni ferment unleashed by the Ayatollah Khomeini.

Those same Arab states profess their lack of faith in western, and especially American, will to defend them. But they hesitate to allow the West the bases on their territory needed to make believable any commitment to defend them from aggression from aboard or subversion at home.

Nor do they much believe in the Carter administration's nostrum that they should form a loose alliance with the Israelis since they are all anti-communists.

Theirs is a more tortuous appraisal based on the realization of their own weakness and wariness about easy solutions to problems which every day grow more complicated. Theirs also is a very real problem of commitment to the Palestinians which the ayatollah's militant support has made inescapable.

The only solace for the West is the knowledge that the Soviets have even greater difficulties in dealing with the same problems. If nothing else, the West can be glad that as the 1980s begin it is the Soviet Union and not the United States which is bogged down in Afghanistan. For that is a messy situation smacking uncomfortably of America's own involvement in the 1960s and 1970s in Vietnam.

American forbearance in Iran, whatever the reasons behind it, at least has the merit of appearing to elevate restraint to a political virtue.

Whether the West manages to evolve ways of dealing with such Third World messes short of military force is devoutly to be hoped, but far from sure.