Boston — ''Three areas are sacrosanct when it comes to determining if a school is truly independent,'' says John C. Esty, Jr., president of the National Association of Independent Schools (NAIS). They are:
* The right of a school to set its own curriculum.
* The right of a school to hire its own faculty largely independent of state licensing requirements.
* The right to express its own philosophy of education and life so long as this philosophy is lawful, in accord with democratic ideals, and nonsegregationist.
''Any curtailment of the first two necessarily interferes with the accomplishment of the third,'' says Mr. Esty.
''Just what makes an independent school independent is a large question,'' says Michael Guerra, executive director of secondary schools for the National Catholic Education Association (NCEA). ''But substantial agreement exists between nonsectarian independent schools and religiously affiliated ones on this issue.''
''A school must be able to express its philosophy and any limitations on curriculum or the freedom to hire would interfere with the articulation of that philosophy,'' says Mr. Guerra.
The NCEA comprises 80 percent of the private schools in the United States. It educated 3,094,000 students in the 1981-82 academic year in more than 1,500 secondary and 8,000 elementary schools. For the same academic year there were 905 NAIS member schools with a total enrollment of 381,654.
One area where disagreement does exist between these two representative organizations of mainstream sectarian and nonsectarian private schools is tuition tax credits.
NAIS opposes tuition tax credits for a number of reasons. But the main one is that ''at a time when public education needs all the support it can get, it doesn't seem appropriate to do anything that takes money from the public schools ,'' says Mr. Esty.
The NCEA thinks differently. ''We see tuition tax credits as a relationship between parents and the government, not the school and government,'' says Mr. Guerra. ''There is no evidence that tuition tax credits would lead to a mass exodus of students from the public schools. Catholics we have a stake in the public schools. We can learn about effective schools from each other. Fifty percent of all Catholic students are in public schools.''
Most proponents of independent schools point out that government regulations force a consistency on the operation of schools that runs counter to individual expression and freedom of choice. They cite this as one of the greatest dangers to any adoption of tuition tax credits.
One spokesman for private schools, requesting anonymity, sees an inconsistency in wanting to be independent and still have federal money.
Fifteen years of Title I experience have convinced many educators that federal rules, evaluation, and ultimately meddling will go hand in hand with any tax credits, no matter what is said or written into the law.
''Largely speaking, private or independent schools have brought a rich diversity to our society, for everyone,'' says Gary Jones, undersecretary of education at the US Department of Education. ''The Reagan administration has attempted to encourage the continuation of this diversity because people choose these schools.''
''But,'' Mr. Jones adds, ''it is not the federal obligation to make sure these institutions survive; the recipients of the education they provide should do this. We just don't want federal government regulations to work against these institutions' survival.''
''Critics of tuition tax credits say the money goes to private schools, but the fact is, the money goes to parents of students who attend schools. The Reagan administration sees itself as providing tax equity,'' says Mr. Jones.
In general, when there must be government involvement, most private schools prefer it at the state level.
''The state government, not the federal, has the responsibility that an informed citizenry be educated, be developed,'' says Daniel Kahn, headmaster of the Anshe Emet Day School in Chicago. ''It can have a set of general standards concerned with this end product, but the ultimate responsibility for education lies with the parent.''
''And from the point of view of parents, the most important component of an independent school,'' says Mr. Esty, ''is decent human beings who care about their kids at a high level of quality instruction.''
Another rationale used for regulating independents is compulsory attendance laws.
Many independent schools have no problem with state laws that set the number of days a child is to spend in school. But they do not feel this is a legitimate reason to regulate curriculum and teacher licensing, because the compulsory attendance law was not designed tor regulate such broad and diverse groups as private and independent schools.
''Government should be involved in the area of health and safety when a child is at school, but not much more,'' says Mr. Kahn. ''Given the ideal, I would hope that they (state government) would leave us alone in large measure, and ensure only that we devise good and effective accrediting agencies of our own.''
At present many independent schools have dual accreditation through regional associations and NAIS or NCEA.