Teachers in the nation's second-largest school district went on strike Monday for the first time in 19 years, abandoning their classrooms for picket lines around the city's 600 campuses.

Informal telephone talks late Sunday between district and union officials failed to produce enough progress on a new contract to warrant calling off the strike, but early Monday there was hope the walkout affecting 600,000 students would be short."We're talking (on the telephone) and playing around with various combinations of numbers but there really has been no movement," said Wayne Johnson, president of United Teachers-Los Angeles.

"(But) I'm still hopeful . . . (Monday) or the next day we will come up with something that is acceptable to both sides," he said.

Pickets began appearing shortly after dawn at the 600 elementary, junior and senior high schools in the Los Angeles Unified School District, the nation's second largest public school system behind New York City.

Teachers last walked out for 23 days in 1970.

School officials attempted to keep schools running with credentialed administrators and hundreds of replacements hired since last week.

Union spokeswoman Catherine Carey said district officials "don't have a chance of hiring enough substitute teachers."

"They're going to herd the kids into auditoriums and gyms and entertain them with movies," she said. "That's not education."

Lt. Frank Valdez, watch commander in the Police Department's gang-plagued 77th Street Division, said he was concerned about security both on and off campus during the strike.

"The problem kids . . . are not going to go to school and it's going to create problems all over, not just on campus," Valdez said. "What I'm mainly concerned about is basically the safety of the other people with all these little predators out on the street."

Valdez said additional officers deployed to keep the peace at the picketing sites would police any increased gang activity on and around campuses.

"If both of them go, we're going to be in trouble," he said.

District spokeswoman Diana Munatones said school police officers have been asked to work 12-hour shifts to avert trouble on the city's 600 campuses with their 600,000 students.

"We don't expect any problems maintaining security, but you never know how things can flare up," Munatones said, adding that the extended shifts enable the district to maintain around-the-clock security at the schools.

The union originally demanded a 21 percent increase over two years. The district offered an 8 percent raise in the first year, 5.5 percent in the second, which would go up to 8 percent with a state financial surplus, and an 8 percent pay hike in the third year.

The union initially threatened to go on strike at the end of May, but members voted to strike Monday after school Superintendent Leonard Britton threatened to withhold paychecks if teachers failed to submit student grades by then.

Johnson predicted 20,000 teachers would walk off the job. Following two hours of morning picketing, teachers scheduled rallies at eight regional parks throughout the city.