SUMMER READING ISSUE : Voices Out of Our Mean Streets : FICTION : THE CONCRETE RIVER,<i> By John Shannon (John Brown Books: $12; 190 pp.)</i> : PERDITION, U.S.A.<i> By Gary Phillips (John Brown Books: $13; 260 pp.)</i>

Call them whydunits--mystery novels with a progressive political slant.

In “The Concrete River,” John Shannon writes of a contemporary Los Angeles with rainy winter skies, “abandoned plants,” idle fishing boats, “a slum that rivaled South Africa” and residents infected by a “grievance they can’t put their finger on,” a “disease of anger.”

Shannon’s hero, Jack Liffey, thinks he knows why: In the 1990s, he muses, “nobody gave a damn, nobody was putting anything but token effort into fixing things, as a sort of social entropy carried the whole country down into chaos. The poor suffered, the rulers turned their backs and the rich retreated into armed enclaves.”

Liffey is a 50-ish, laid-off aerospace worker, divorced and recovering from a bout with drink and drugs. He scratches out a living in Culver City as a private eye who specializes in finding missing children. Murder cases are out of his league.

But when a Latina activist is found drowned in a storm drain, her mother hires Liffey to investigate. The trail leads him to the barrios of Cahuenga (East Los Angeles), to romance with an ex-nun turned social worker, Eleanor Ong, and to a showdown with a BMW-driving, corn pone-joking killer called the Cowboy.

Shannon (“The Taking of the Waters”) writes stories with a bleak, European, existentialist feel, mixed in this case with absurdist touches: Styrofoam cups and tennis balls clogging Ballona Creek after a storm, disabled men pummeling each other with prosthetic limbs, traffic-jam arguments that “go nuclear.”

Most Americans still like to believe that no one is beyond the law, but Liffey knows he has no hope of laying a glove on the billionaire gambling and development moguls who hired the Cowboy. He is hot-tempered, decent and stubborn enough to pursue his lonely quest anyway. He tells Ong: “Being a detective is a kind of faith in life, isn’t it?”

This is the first of a projected series of Liffey mysteries, which Shannon says will deal with Los Angeles social history much as the Martin Beck mysteries by Maj Sjowall and Per Wahloo dissected Stockholm in the 1970s.

In “Perdition, U.S.A.,” Gary Phillips has his black private eye, Ivan Monk, investigate the killings of African Americans in Pacific Shores, a rundown industrial area resembling Wilmington, by skinheads linked to a nationwide white-supremacist group, the War Reich.

The victims, petty hustlers and drug dealers, arouse little sympathy. Even Monk, hired by one of their girlfriends, a “struggling teenage mother” named Clarice Moore, is at first inclined to write the murders off as routine gangbanging.

Besides, Monk fears that “the resolution of the puzzle . . . wouldn’t make the future any brighter” for Clarice or anyone like her in an age of “no-butter, more-prisons politicians,” when “the cellular phone set” ignored the poor as they “jockeyed for position to catch the rising wave of Chinese capitalism on their Sharper Image surfboards.”

He remembers his father’s words all too clearly: “When we do get a peek at the rule book, them cracker bastards are laughin’, ‘cause they ain’t even goin’ by one.”

But Monk takes the case anyway. It leads him to Perdition, a town in eastern Washington state where old right-wing money and trendy doctrines of hate form an explosive mixture.

By the time he’s finished--a little the worse for wear--Monk has dealt with garment sweatshops, a phony-watch sales ring, a band of “multiracial skinheads” who trade punches and Doc Marten stomps with the bad guys and a plot to assassinate a liberal U.S. senator.

Monk first appeared in “Violent Spring,” a mystery that opened with the discovery of a body buried at Florence and Normandie, flash-point of the 1992 Los Angeles riots. It was often awkwardly written, but it had huge, Dickensian ambitions: Phillips, a longtime activist and Compton Bulletin columnist, stuffed most of L.A.’s neighborhoods, classes and ethnic groups between its covers.

The prose in “Perdition, U.S.A.” is rougher, if anything. The plotting is baroque, to say the least. It might be counted a mistake to let Monk wander so far from his South-Central turf. But it’s also a sign of Phillips’ continuing hunger for the big picture.

Monk is an asset to the series--flawed, human, angry but level-headed, brainy and brawny. Unlike Liffey, he has plenty of relationships going--with his white mentor, Dexter Grant; his Japanese American girlfriend, Superior Court Judge Jill Kodama; his schoolteacher sister; and the former down-and-outers who work at his Crenshaw district doughnut shop. Monk is part of a community--though it’s a community that these days feels threatened from all sides.