''Roll out those lazy, hazy, crazy days of summer.'' The words of the old Nat (King) Cole hit conjure up memories of the golden months spent in summer sports, romance, or jobs before school opened again in September.
Yet thousands of students in public schools around the country will not enjoy a vacation this summer. These students attend year-round schools in districts that face severe overcrowding, most of them in the Southwest United States.
Under the year-round plan, students attend school in three or four ''shifts'' throughout the entire year. Each shift, or track, has a different vacation time. By staying open during the summer months, the school can pack in one-fourth to one-third more students every year.
Overcrowding in public schools is fast becoming a problem unique to the Southwest. Although overall enrollment in public elementary and secondary schools has declined steadily since 1971, a general population shift toward the South and West has dramatically boosted school enrollment in those states.
For example, Washington, D.C., lost 25.5 percent of its students in the 1970s , but school enrollment in Nevada went up 13.5 percent. And in a similar shift, Baltimore County, Md., reported an annual loss of 5,000 students over the last decade, compared with an annual gain of 3,800 students in the state of Utah.
The increase in school enrollment in the Southwest also reflects the heavy Latin and Asian immigration into these states and the high Latin birthrate there. In combination with white flight to private schools and a low white birthrate, these factors can create a double dilemma of underenrollment and overcrowding within the same school district.
The Los Angeles Unified School District, for example, is running dozens of underenrolled schools in the heavily white Westside area and San Fernando Valley - at the same time that schools in the Hispanic and black southeast and south-central city neighborhoods are bursting at the seams.
As a solution to overcrowding in Los Angeles schools, busing of minorities to underenrolled white schools is not popular. Hispanic communities traditionally oppose busing schoolchildren outside their neighborhood; and they remember that the school board and its white constituents in the San Fernando Valley successfully opposed court-ordered busing for integration last year.
Claiming a shortage of funds for new construction, the Los Angeles School Board has thus opted for what it says is the best answer to overcrowding: the year-round school.
In California, 42 districts have implemented the year-round system in one or more of their schools. Nationwide, there are about 350 of these schools, serving 278,000 students - an increase of over 35,000 students from last year.
The Los Angeles Unified School District alone expanded its year-round schools from 42 to 82 for the 1981-82 school year, affecting a total of 120,000 students , most of them minorities. Los Angeles now has more year-round schools than any other district in the country. California districts planning to implement the year-round school or looking into the idea include Lynwood, Lennox, Alhambra, and Fontana. The Houston, Texas, school district and districts in New Jersey, Rhode Island, and Minnesota are reportedly exploring the year-round school calendar.
When year-round schools were first put into practice 10 years ago, they were seen as a way to improve the quality of education. Parents chose the new system because they felt it would reduce ''summer learning loss'' by giving students shorter, more frequent vacations. Now the concept has changed.
''Right now,'' says Vincent Laura, coordinator of the overcrowded schools task force of the Los Angeles Unified School District, ''schools are going year-round because they're overcrowded.''
Districts that impose the year-round plan to reduce overcrowding have not found the going easy. The expansion of the year-round schools in Los Angeles, for example, sparked protests last fall in the heavily Latin southeast and east Los Angeles communities, where most are operating.
A glance at the year-round schedule indicates just how complicated this system can get. At the high school level, students are divided into three tracks , each with a different starting date and different vacations. Tracks A and C run for four months and then break for two. Track B has a two-month break in the middle of each semester. To make up for 13 fewer days of school each year, students start classes at 7:30 in the morning instead of the usual 8, and receive an additional 10 minutes per period.
In effect, administrators are running three small schools instead of one big one on each high school campus. Scheduling problems, then, have tripled. If there is only one teacher to teach a given subject, that subject can be offered on only one track.
The dilemma facing Bertha Garcia, an 11th-grader at Huntington Park High School, is a common one. She needs trigonometry and physics to get into college, but neither course is offered on her track. To take these subjects, she has to go to school during her off-track vacation time.
''I'll be going to classes all year,'' she says.
Other top students, like Teresa Argeaga, a sophomore at Huntington Park High, have been unable to get into the advanced level courses they qualify for. Teresa is taking regular biology because the more advanced academically enriched (AE) biology course was full. Next year she wants to take advanced placement (AP) history, a course which will prepare her for a national exam for college credit. However, the course is not offered on her track.
The scheduling problems inevitably give rise to academic tracking - in practice, if not officially. Students interviewed said most of the AE and AP classes are on A track. They pointed out that A track students were the only ones able to take college courses during the summer, since their track didn't start until September.
''My friends on B track,'' notes Guillermo Castaneda of Huntington Park High School, ''are not computers. They have to spend most of their vacation just trying to keep up and not forget everything they're studying. It's not the greatest vacation on earth.''
On the extracurricular side, students lamented the lack of a ''sense of belonging'' on campus and spoke of their ''feeling of disenchantment.''
''Part of being in school is the clubs and student government,'' say Edward Jai, a senior at Belmont High, ''and so far these activities haven't been reconciled to the year-round school.'' Jai pointed out that some tracks get disproportionately more activities and have more representatives on the student council than others, and that students have to come in during their vacations to take part in sports.
In fact, students on the gymnastics team at Huntington Park High School received notice that they would be dropped from the team if they did not attend practice during their off-track vacation.
At South Gate High School, sophomore John Olivas went to band practice every day while he was off-track, and admitted the band has ''had problems'' functioning.
Belmont High's Mauricio Gonzalez notes that since colleges look at the extracurricular activities of applicants as well as their grades, the year-round student has to carry a heavier load. As student body president, he feels obliged to continue his extracurricular activities during his off-track time, on top of taking AP Spanish.
''But why should I have to spend more time in school than other kids (in regular schools)?'' he asks. ''Year-round school just makes it harder for a potential candidate to a big college to get things done.''