For Barbara Coe, everything changed the day she accompanied an elderly friend to an Orange County social services center in 1991.

"I walked into this monstrous room full of people, babies and little children all over the place, and I realized nobody was speaking English," the South Dakota native later told the Washington Post. "I was overwhelmed with this feeling: 'Where am I? What's happened here?'"

When she learned from a welfare counselor that immigrants who had entered the country illegally qualified for the same public benefits that had been denied her friend, a U.S. citizen, Coe began her journey from political neophyte to fiery crusader against the demographic tide that was transforming California.

Coe, 79, who helped lead the grass-roots movement behind Proposition 187, the controversial 1994 state ballot initiative to deny those in the country illegally access to basic public services, died Saturday at her Huntington Beach home. The cause was cancer, said Evelyn Miller, a board member of the California Coalition for Immigration Reform, which Coe headed.

"She was fire and brimstone," said Glenn Spencer, who worked with Coe on the Proposition 187 campaign and now heads the Arizona-based group American Border Patrol. "She understood the issues and was a fighter."

She had many detractors, but even opponents acknowledged her success.

"She was certainly an aggressive and effective advocate in the anti-immigrant movements ... and kept alive anti-immigrant initiatives every few years, it seemed," said Peter Schey, director of the Center for Human Rights and Constitutional Law and a co-counsel in the lawsuit that blocked Proposition 187. "Those weren't initiatives I felt were particularly good public policy or very humane."

Coe, who was born on a Sioux reservation in South Dakota on Dec. 6, 1933, was a crime analyst for the Anaheim Police Department until she took on her high-profile role at the forefront of the Proposition 187 campaign. She told friends that her superiors in the Police Department disapproved of her activism and demoted her.

A representative of the Anaheim Municipal Employees Assn. who tried to help Coe save her job told The Times in 1994 that Coe got into trouble after using a city-owned camera to photograph striking drywallers who were picketing police headquarters. Coe suspected many of the protesters were Mexican nationals.

With Bill King, a former Immigration and Naturalization Service agent, Coe formed Citizens for Action Now in 1992 after advertising a Costa Mesa meeting of "everyone concerned about the illegal aliens problems." Nearly 40 people showed up at the meeting to hear the featured speaker — the Orange County welfare office worker who had complained to Coe about public services given to immigrants.

Coe then formed the California Coalition for Immigration Reform with Tustin accountant Ron Prince, who pushed the idea of a statewide petition drive that put Proposition 187 on the ballot.

The measure sought to ban unauthorized immigrants from public schools and universities and block them from receiving social or welfare services and publicly funded healthcare except for emergency treatments. Its supporters argued that it would save the state money and help stem illegal immigration to California. Coe and Prince called the measure the SOS (Save Our State) Initiative. Its coauthors included two former federal immigration officials, Harold Ezell and Alan Nelson.

Shortly before the 1994 general election, Coe announced plans to post "Only citizens can vote" fliers near Election Day polling places, which brought accusations of voter intimidation from Latino activists. She was interrogated by an FBI agent but never posted the fliers. The investigation was dropped, and Coe remained undaunted.

"I work with immigration issues from early morning until late at night," she told The Times in 1995. "It is my position that we are on the verge of losing the sovereignty of our nation, and we need to fight that."

She crisscrossed the country to speak to like-minded groups, including the Council of Conservative Citizens, which civil rights activists have labeled a white supremacist group.

In 2007 Coe was embroiled in a fight over the leadership of the Minuteman Project, the citizen border surveillance group. She and two other directors of the group ousted its founder, Jim Gilchrist, over allegations of financial impropriety. She later resigned from the board.

Coe's survivors include a son, a daughter and grandchildren.

elaine.woo@latimes.com