It is hard to know whether one is awake or asleep....Motion is slow as a dream"". These words, overheard at the U.N. where most of Miss Buckmaster's novel takes place, indicate the general tone of inaition here even though this deals with a new (post-Vietnam) crisis in one of the airpockets of the Cold War. Mongolia has abrogated her pact with Russia and shifted toward Red China, setting in motion the whole machinery of U.N. debate and negotiation (although some 250 pages later--this is a very long book--neither of the big powers has moved). Walking reflectively down the corridors of power is Secretary -General Devar: he's Ceylonese, with Hammar-skjoldian markings, pursuing the obliquities (a favorite word here) of diplomatic amenities as well as other moral and metaphysical chimeras. On the political side, there are only two episodes to follow the initial impasse: the shooting of an Irish delegate; and the inadvertent (?) dropping of a bomb by China. On the personal side, there is Devar's inadmissible love for his best loved brother's wife, who has temporarily left him. By the close the situation is resolved and a new war averted, and Devar, the ""holy man."" the mediator committed to ""humankind, "" concludes that we have ""nothing but persuasion, nothing but love"" to reveal the lion in the stone. . . . For all its altitudinous intentions, its sweetly reasoned and discreetly articulated concern, the novel, per so, is a tendentious defente.