CALIFORNIA ALBUM : An Isolated, Sleepy Town--and a Shocking Aberration : Weeping willows and magnolias grace San Jacinto, where folks savor a Midwestern lifestyle, now shattered by the murders of three children.

If a town is reflected by its police blotter, consider some of last Thursday’s entries:

A cow sitting on the side of the road. A traffic stop--warning, no ticket. A stolen welfare check. Kids throwing objects at passing cars. Someone trying to lift up a manhole cover. Several family disturbances.

And one read, simply, “triple homicide.”

Such an unspeakable crime--a 34-year-old woman who allegedly stabbed her three young children to death--would seem an aberration for any community.

But perhaps most of all, here.

Surrounded by handsome dairies and sprawling horse ranches, this oldest of Riverside County’s cities, population 23,000, embraces an ambience seemingly plucked out of the Midwest, something as close to Mayberry as you’re apt to find.

Folks sit on their front porches, facing avenues lined with weeping willows and magnolia trees. Downtown, with its mom-and-pop stores, is unencumbered by parking meters. A five-way intersection is governed only by stop signs.

The two-story Virginia Lee Hotel, built in 1884, is now a weekend bed-and-breakfast inn, but available during the week for fashion shows and teas. Kids ride bicycles down the sidewalks and past the local Tastee-Freez and the high school homecoming parade is routed through the center of town for everyone to enjoy.

There’s no bowling alley here, no miniature golf, but there are five parks. Although a 12-screen movie complex is under construction, there hasn’t been a theater in town for decades.

That old theater was where W. C. Fields sat in the back row and spat tobacco juice, back when Hollywood stars came here to indulge in the local hot springs, before Palm Springs--on the other side of the mountains--became the chic Angeleno resort.

McDonald’s didn’t even come to town until two months ago.

“It’s very definitely a quieter lifestyle than you’ll find in, say, Orange County,” says Mayor Henry Hafliger, a dairyman who has lived here 30 years.

The cops here like the lifestyle. Two came from the Los Angeles Police Department. Another left the Los Angeles County Sheriff’s Department to work out here. The chief came here years ago from the city of Orange, and brought a couple of officers with him.

Last week, they worked late into the night to try to figure out who killed the Buenrostro kids--4-year-old Deidra, 8-year-old Vicente and 9-year-old Susana.

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All day Thursday, police interviewed Dora Buenrostro, who that morning had stormed into the police station, seeking help because, she maintained, her estranged husband had shown up and she feared for her children’s safety.

When an officer returned to her apartment, he found the stabbed bodies of the two older children on a blood-soaked living room couch.

Buenrostro alleged her husband killed them. But he lived and worked in Los Angeles and had an ironclad alibi, police concluded.

They fed her lunch and they fed her dinner and they kept asking her if she knew where her youngest child was. Her answers were cool and evasive, said Riverside County Deputy Dist. Atty. Richard Bentley, who listened in.

Later that evening, youngsters found Deidra’s body, strapped in a car seat, inside an abandoned, rural post office building strewn with broken glass. She had been stabbed in the neck, like the others.

At 2 a.m. Friday, police arrested the 34-year-old woman with wavy brown hair falling past her shoulders. Her statements to police were inconsistent, Bentley said. Her arraignment is scheduled Nov. 10. Bentley said he will prosecute her on three counts of murder, and he is thinking of asking for the death penalty.

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In the patio of the Buenrostro one-story garden apartment, two bicycles, a red-and-white trike, green roller skates, a doll and a football were still neatly arranged after the yellow crime tape had been removed from the scene.

Neighbors tried to make sense of the crime. Some just decided they couldn’t.

“We’re just like family and we don’t want to talk about it,” said one woman. She broke into tears and excused herself.

“I still don’t think it was her,” offered Manuela Villareal. “Maybe it was drugs.”

Bill Brudi said he used to fly kites with the children.

“The kids were always dressed nice, didn’t sass anyone back, and their mom would take them to church twice a week,” he said.

Velia Cabanila was more suspicious. She lived in the same four-unit building and could hear, she said, plenty of shouting and yelling through the wall. And she’d let the Buenrostro children use her bathroom when their mom was gone and they were locked out of their own place.

Cabanila said she didn’t hear anything unusual the morning that police found the bodies. Just a thump, about 3 in the morning.

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At Hyatt Elementary School, where Vicente was a third-grader and Susana was in fourth grade, the office staff last week photocopied handouts, “Some Basic Guidelines to Help Children Deal With Death.”

On Tuesday, Principal Deborah DeForge was making tentative plans for an on-campus memorial service for the Buenrostro children, a catharsis for the other youngsters and teachers.

Susana was the shy, quiet one of the two, DeForge said. She hoped to become a dancer or singer. Vicente was the funny one, always laughing and teasing others. Both were athletic.

Last Thursday afternoon’s Blast to the Past school dance was held as scheduled. “We want to keep the routine as much as possible,” DeForge said. “The kids need something to rely on while they’re dealing with the grief of this tragedy.”