ALTURAS, CALIF. -- Why tiny Modoc County, population 9,673, should have such a grip on the political consciousness of this megastate remains as mysterious as the lava caves where 75 Modoc tribal warriors held off 1,000 federal troops a century ago.

Modoc voters have picked the winner in all but two California gubernatorial elections since this northeast corner of the state became a county in 1874. They have done so despite having almost nothing in common with the city and suburban residents who form the bulk of California's population of 30 million. The 1980 census in Modoc found only 14 blacks, and Hispanics accounted for barely 4 percent.

Four miles northeast of this county seat, on 500 acres of sagebrush and juniper called Hidden Valley Ranch, county Supervisor Don Polson and his wife, Beverly, offered a hint of what keeps Modoc so close to the political mean. "People are not that interested in state and national politics," Polson said, taking a break from painting his kitchen. Party labels have little importance, and organized interest groups are rare, he and other longtime residents said. As a result, Modoc has a political elasticity not found in bigger and better-organized counties.

Modoc residents also are relentlessly fair-minded. The Polsons are Republicans who support this year's GOP gubernatorial candidate, Sen. Pete Wilson, but they also admire his Democratic opponent, former San Francisco mayor Dianne Feinstein. "I think she came across as much more intelligent in the debate," Polson said of a recent Feinstein vs. Wilson telecast. "I wasn't embarrassed for Wilson, but I wasn't very proud of him either."

That is not to say that people living on this vast prehistoric lava flow are unfamiliar with conflict, political or otherwise. The Dorris family, Tennessee cattle ranchers who originally settled the area, had trouble persuading local Indians to vacate the high grass and plentiful water of the Pit River Valley. The Modoc tribe fought one of the costliest Indian wars in U.S. history from its lava fortress at the Stronghold to protest being moved to a reservation in Oregon. This became Modoc County -- rather than being named Canby County in honor of an army general killed in the war -- because a state legislator who wanted to kill the bill thought that his colleagues would not vote to create a county with such a bloodstained name.

The county retained its Wild West flavor. A detailed history in the little county library reports "a twenty-man posse clothed in barley sack masks" lynched two cattle thieves from a bridge railing over the Pit River May 30, 1900.

Passions still run high when something threatens the leisurely pace and breathing room that Modoc people cherish. The governor's race cannot compete with the controversy about a $240 million, 4,000-bed prison that the state wants to build in the county. The 76-year-old county courthouse with a big orange dome was jammed for a public hearing on the matter. Fifty-five percent of the voters rejected the prison proposal, and a bitter division remains between pro-prison business executives and anti-prison protectors of Modoc lifestyles.

The county has lured many retirees to its new California Pines subdivision and has a thriving tourism, recreation and hunting business. "The economy is pretty well balanced with livestock, timber, and we do drink a little," said rancher Rob Flournoy, standing outside an Alturas tavern.

The county's 2,495 Democrats, including ranch hands and mill workers, outnumber by 100 the Republicans, who include ranchers such as Flournoy. County Clerk Maxine Madison also counted 107 members of the American Independent Party, 23 Libertarians, 18 Peace and Freedom members, 1 Socialist, 1 Prohibitionist and 452 who declined to give a party preference.

"We used to have two Prohibitionists," she said, "but one just died."

Former governor Edmund G. "Jerry" Brown Jr. joked when elected Democratic Party chair last year that the news media were unlikely to cover his visits to Modoc, and indeed there is little evidence that he has set foot here. The Democratic county committee is nonexistent. Jim Chapman, treasurer of its struggling counterpart in neighboring Lassen County, said people in small rural towns resist partisan activity because they know everybody "and do not want to expose their friendships and business relationships to that kind of intensity."

Brown has had trouble here. Madison said he is the only winning gubernatorial candidate who never carried the county. Modoc's first failure to uphold its bellwether reputation, in 1974, can be traced to the fact that Brown's opponent was Houston Flournoy, a distant relative of the many Flournoy descendants of French Huguenot settlers in Modoc. Brown's failure to carry Modoc against another candidate in 1978 is harder to explain. Madison will say only that voters "knew more about him then."

Since that lapse, Modoc has given Gov. George Deukmejian (R) large majorities in his two winning races and also backed Feinstein in her victorious primary race in June. But if an unscientific Washington Post survey of 100 Modoc voters can be believed, she may be in trouble here in November.

Among intense Feinstein supporters is Patricia Burkett, who said while browsing in the library, "Men will talk about it, but women will do it." Far more residents echoed the sentiments of chiropractor Randolph Waugh: "Wilson probably lines up more with my way of thinking." The survey's results: Wilson 44, Feinstein 32, undecided 24.

Feinstein may suffer from her support of Proposition 128, an environmental initiative that many people think will hurt the timber industry. Fortunately for her, not everybody in Modoc County pays attention to such things.

County Supervisor Melvin Anderson, whose liberal leanings have earned him the nickname "Tip O'Neill," runs a logging outfit and seemed unpleasantly surprised to hear that Feinstein supports Proposition 128. But like any good Modoc County voter, he judges the person, not the politics. "I'll still vote for her," he said.