THE DISTINCT possibility now exists that Amadou Mahtar M'Bow, the Senegalese who more than anyone brought UNESCO to its current low state, may shortly be in a position to administer the coup de gra~ce. Widely identified with the politicizing and the mismanagement of UNESCO, he had said he would not run for a third term as director general, but he is. If he is reelected, the number of nations following the United States and Britain out the door will grow, and UNESCO will face terminal drains of funds, participation, prestige and usefulness.

The 50 members of UNESCO's executive board meet in Paris next week to nominate a candidate for the full membership's later confirmation. Mr. M'Bow, playing on African regional sentiment and using the patronage power, appears to have 18 to 20 votes -- short of the necessary majority. Somewhat fewer votes are claimed by Pakistani Foreign Minister Sahabzada Yaqub Khan, who is well known in diplomatic life but whose military past lowers his standing in Latin America and elsewhere. The dark horse is Federico Mayor, a Spanish biochemist and former education minister whose advantage and disadvantage is that he served as Mr. M'Bow's deputy.

The M'Bow candidacy rides on the reluctance of many nations to allow even the baldest evidence of unfitness to interfere with bloc logrolling. Still, an alternative is conceivably in reach. To counter the M'Bow early-ballot strategy, the Europeans (and Japan) now seek to have the executive board stretch out the balloting and to open the contest to candidates who might come in if no announced candidate got an early majority. They have in mind Enrique Iglesias, a development economist of world standing who is democratic Uruguay's foreign minister. He reportedly feels that to have to employ the usual narrow, divisive and often sordid tactics of bloc politics to win the post would make it not worth winning. There is reason to believe, however, he would consider a consensus draft.

Whether UNESCO can ever reform itself to the point that the United States would contemplate rejoining is a question that engages few Americans these days -- certainly not very many in the Reagan administration. The (Democratic-controlled) Congress is unwilling to pay in full even for U.N. activities of which it approves. But the necessary prior question is whetherUNESCO's Third World members have any serious intent to save it in order to help recreate the international culture of the mind that was the organization's founding inspiration. The voting for director general will tell.