ROBERT STONE's third novel is sweeping and ambitious. It deals with major political and social themes; it is set in a small, backward, near-mythic Central American country; it has a large, diverse cast of characters whose fates draw them inexorably to the same place at the same moment; it invites comparison, according to promotional material, with For Whom the Bell Tolls and The Naked and the Dead.

Since both those novels are vastly overrated, the comparison is apt. Notwithstanding all the baggage it carries, A Flag for Sunrise has little to recommend it. Stone writes very well, he creates plausible characters, and he has a deft hand for dramatic incident. But he is a preacher masquerading in novelist's clothing, indulging himself in rhetoric right out of SDS or the IWW. It is the politics of his novels rather than the craft of them that seems ultimately to interest him the most; the problem is that there is nothing interesting about his politics.

The setting is Tecan, a country of which a native remarks: "There's nothing but failure here. The country is a failure. A disaster of history." It is ruled by a dictator who hides from his countrymen in a palace walled off by barriers and his omnipresent police, the Guardia. But revolution is in the air; guerrillas are gathering in the hills, preparing for a surprise offensive that is expected to leave the president isolated and vulnerable.

It is a situation rife with danger and ripe for exploitation. At the tiny settlement of French Harbor, two American missionaries--Father Charlie Egan and Sister Justin Feeney--are increasingly aware of the menacing presence of the Guardia on the one hand and the restive populace on the other. The Guardia suspects that the missionaries are giving clandestine support to the rebels, and relays that suspicion to the government of the United States, of which Tecan is--but of course--a client state. So when an American anthropologist named Frank Holliwell prepares to deliver an address in the neighboring country of Compostela, he is approached by an old friend, now working for American intelligence, and asked if he would mind dropping over to Tecan and having a look at French Harbor.

While all of this is going on, an exceptionally vile young man named Pablo Tabor is making a thorough mess of his private life and his low-level Coast Guard career. He leaves it all behind him and eventually works his way to Compostela. There he is hired by Jack and Deedee Callahan, an American couple languidly radiating wealth, to crew on the shrimp boat they ply about the Gulf. But--of course--it is not a shrimp boat at all; the Callahans, cynical Americans that they be, are running guns for a profit to the rebels of Tecan.

The convergence of all these people--not to mention others too numerous and insignificant to bother with--is entirely predictable. One small case in point. Early on we are told of Frank Holliwell: "He was . . . really without beliefs, without hope--either for himself or for the world. Almost without friends, certainly without allies. Alone." Early on we are also told that Sister Justin is both beautiful and troubled. Almost 400 pages before it happened, I knew for a fact that they would find a way into bed together. A more clich,ed situation would be difficult to imagine.

Sister Justin is clearly intended to be the novel's moral center, but she is simply too good to be true. When Holliwell meets her: "He avoided looking her in the eyes; it was harrowing because she could conceal nothing. Along with the fear, mastering it was a mighty pride. More was what drove her. Whatever the world afforded in the name of virtue, sacifice, good works--she wanted more, wanted it all, as though she deserved it. She could be clever, she could play a little homely poker but she had never learned to trim the lights of her pride." A saint, in other words, with a bit of earth on her shoes. It's too much.

So is the novel's rhetoric. At one point the aging leader of the revolution confronts his heir apparent, and asks if there might not be some cynicism in his ambition. Without a trace of irony, Stone has the younger man respond:

"Cynicism? That I--a plain man, a mediocre artist, perhaps even a mediocre fighter--take it upon myself to bring justice to our accursed suffering country? To bring health to her children, dignity to her desperate poor? To replace her absurdity in the eyes of the world with pride --to make housing, hospitals, schools for her masses of ignorant? To leave sound philosophy and engage life which we both know to be so vulgar? To dispense life to some and death to others in the name of a form of humanity which for all we know may never exist?"

Viva Zapata!

Stone's posturings are one thing, the problems and suffering they attempt to address quite another. A novelist's windy sentimentality may be laughable, but conditions in much of Central America are deplorable. Yet Stone trivializes what he hopes to glorify. The stock roles that his characters play and the stock rhetoric that they utter are nothing more than safe, comfortable responses to a situation that is considerably more complex and ambiguous than Stone appears to realize.

When Stone gets off his soapbox and pays attention to the craft of fiction, he is very good. He is also haunted by Vietnam, and he makes a penetrating connection between the ghost of Vietnam and the agony of Central America. At one point he writes: "Smaller breezes stirred against the sea wind's breast, carrying an iodine smell, a smell of jacaranda, of flowers he knew by half- forgotten, six-toned names from across the world--me- iang, ving, ba--the smell of villes in Ban Me Thuot, cooking oil, excrement, incense, death. The smell of the world turning. War." That is good.

So long as Stone sticks to observation and characterization, he is a very effective writer--as he was in his second novel, Dog Soldiers, which won a National Book Award. But here he is so much the preacher that the novelist almost disappears. The sincerity of his convictions is transparent, but his rhetoric is tiresome. So is A Flag for Sunrise.