Overcrowding at Los Angeles secondary schools has become so acute that the district is considering converting up to 25 campuses to multitrack schedules to alleviate a projected shortage of 8,600 seats for the coming school year.

Setting up portable classrooms at crowded junior and senior high schools was another option included in a report presented Monday to the Los Angeles Board of Education. Schools were also urged to submit creative proposals to solve the space crunch.

More classroom space is urgently needed "to prevent a difficult housing problem from becoming a full-blown crisis," Joyce Peyton, a district administrator who helped compile the report, told the board.

Peyton said the district expects 13,500 new secondary school students by 1993 and must increase capacity at schools by 23% to meet the demand. Under a multitrack system, campuses can accommodate up to one-third more pupils by dividing the student body into groups that attend school on staggered schedules, with one group on vacation at all times.

Overcrowding is most acute at junior and senior high schools in the east San Fernando Valley, South-Central Los Angeles and southeast, she added.

In part, the crowded conditions at secondary schools reflect the movement through the system of children who poured into the elementary schools several years ago.

The district expects overcrowding will occur at more high schools as students are bused from campuses already at capacity. In addition, high school students who require special education programs will jump by 8,000. That will place a disproportionately large strain on the district because special education classes average 10 students each.

The district must also comply with a new state law that limits certain high school math and English classes to 20 students each.

The overcrowding comes when no junior or senior high schools are under construction and the district is desperately searching for alternatives.

"There aren't a lot of choices, but the schools understand the situation we are in and they want to do something," Peyton said.

In a controversial decision aimed at relieving overcrowding, the district voted earlier this year to convert all of its approximately 645 campuses into year-round schools by July, 1991.

Monday's report took the concept of year-round schools further, suggesting that overcrowded high schools also implement multitrack programs.