Democracy: A Novel, by Joan Didion. New York: Simon & Schuster. 234 pp. $13.95. THE title of Joan Didion's fourth and newest novel may seem at first inappropriate, melodramatic. Its most obvious reference is to Henry Adams's ''Democracy, An American Novel,'' concerning the political corruption of the administration of President Grant. Didion's book, occurring primarily during the Vietnam years, centers on an American family of businessmen and politicians. But , while Adams's focus may have been the corrupt people who enter the political arena, Didion's is more what she sees as the corruptive nature of public service itself.
Inez Christian Victor, the novel's main character, grew up in Hawaii, married United States Sen. Harry Victor, and had two children - Jessie and Adlai. In 1975 Jessie runs away to find a job in Saigon. At this same time Inez's sister, Janet, is killed - perhaps accidentally - by their father, a trauma which, in part, persuades Inez to flee. She leaves her husband and son to search for Jessie.
In the course of Inez's search, she is reunited with Jack Lovett, with whom, in 1952 at the age of 17, she had had an affair. These events, told in flashback , constitute the novel's plot. But they are not really what the book is about; Didion's theme is democracy, viewed from many angles.
''Call me the author,'' says the narrator at the beginning of Chapter 2, further identifying herself as ''Joan Didion.'' But this ''Joan Didion'' is from textbook essays and newspaper articles - the author as a public persona. As she does with her celebrity-characters, Didion separates the public from the private self.
There is a kind of false ''democracy,'' she intimates, in the public's familiarity with the writer as a personality. Inez and her family have the same difficulty in separating themselves from their media images. This pressure, more than any other, causes Inez's eventual abdication of her position as a politician's wife.
Another instance of ''democracy,'' or its absence, is expressed through the life styles of Didion's characters. As upper-middle-class people, they are insulated by money, fame, and power from everyday difficulties - an ''undemocratic'' way of life. But Inez cannot buy her way out of the tragedies of her immediate family members; she must confront her grief and guilt. So there is a leveling, or ''democratizing,'' element in the novel's outcome. As a parallel event, the 1975 evacuation of Americans from Saigon, during Inez's stay there, provides the novel's climax, and is carried out in order of the residents' social standing - a microcosm in which corruption becomes anarchy.
There are, then, many instances of ''democracy'' in Didion's novel. Her attitude toward it may be summarized by a recollection of a lecture she gave to a Berkeley class: ''Consider the political implications,'' she writes, ''of both the reliance on and the distrust of abstract words.'' Didion is referring, in essence, to the writer's love-hate relationship with words - love of their versatility as tools of the trade but aversion to their variability and, hence, vulnerability to corruption.
Joan Didion, one of our most serious contemporary novelists, has gained a reputation as a ''doomsayer'' for her often-expressed trepidations toward certain social currents of the 1960s and '70s. In ''Democracy'' she provides a more hopeful view. At the novel's conclusion, Inez remains separated from her husband and so for the first time controls her destiny. Previously, she had passively accepted circumstances, much as did Charlotte Douglass, the protagonist of Didion's third novel, ''A Book of Common Prayer.''
There are many similarities between the two books, but, while Charlotte perishes because of her inability to take hold of her life, Inez survives - even though as an outcast - and the narrator, ''Joan Didion,'' expresses some admiration for her refusal to acquiesce.
Such difficult moral choices, Didion seems to say, are sometimes the only way of preserving those abstractions that make our lives worth living. This is a truism equally applicable to democracy and the contents of her novel.