Ending an educational controversy involving thousands of teachers, parents and students, the Prince William County school board has voted to abolish its year-round schools and place all county students on the traditional September-to-June calender.

The board voted 5 to 2 Wednesday night to have all but the Dale City section of the county follow a traditional school term beginning in September. Dale City's nine schools revert to the traditional school schedule in September 1981, a delay requested by Dale City residents.

Initially adopted by the school board in 1971, the year-round system helped Prince William handle a student enrollment that was growing faster than the county could provide schools.

About 65 percent of the county's nearly 40,000 enrollment is on the year-round calendar, which divides students into four groups. Only three of the groupss attend classes at any one time and then for 45-day stretches which the fourth group is on vacation.

"This (the vote) gives us a clear directive for unifying our schools under one system of scheduling rather than a dual system," said school superintendent Dr. William Helton, who had recommended the board return schools to the nine-month calendar.

Helton, who expects the county's school population to level off or decline during the next five years, said the year-round schedule had proved to be exhausting to many teachers and a scheduling nightmare for adminstrators.

Most parents and students from the Dale City area, however, had argued to keep the year-round system and said they found its schedule of three weeks vacation for every nine weeks in class conducive to education and their life style.

School board member Phyllis O'Toole argued against reverting to the traditional calendear countywide, saying no one had yet established which educational method was the best for the students.

Herbert Saunders, one of those board memebers voting to adopt the traditional calendar, urged that the superintendent make another enrollment survey of the Dale City area prior to imposing the traditional calendar on its schools in 1981.

The board's action leaves about 10,000 students on the year-round schedule for next school year, all in the eastern Dale City section of the county. Dale City will be one of the few areas of the country operating schools on a year-round calendar, educators says.