AFTER a nearly year-long, $175,000 test-tampering investigation that drew national attention and badly divided the Fairfield school community, the mystery of whether the Stratfield School principal, Roger Previs, tampered with standardized tests at his award-winning school may never be resolved.

An agreement on March 13 between the 57-year-old Mr. Previs and the school board allows the principal to retire after 35 years in the school system with full benefits and an undisclosed amount of money.

Many parents have defended Mr. Previs and they contended that losing the popular principal was a tragedy, particularly for his 500 pupils. During his nearly 18 years as principal, Stratfield was twice recognized as a blue-ribbon school by the Federal Department of Education

''It's back to mediocrity in education; now we'll be just another public school,'' said Ginny Klinga, a Stratfield parent and member of the Fairfield Parent Association, a group that was formed last April in reaction to the test-tampering investigation. ''Mr. Previs raised public education to a far higher level than we have ever seen before, and the way this entire situation has been handled has been disgraceful.''

Other parents disagreed. ''I applaud the efforts of the board to insure that cheating and lying have no place in Fairfield public schools,'' said a Stratfield parent, Elise Epner, a member of Fairfield's Representative Town Meeting. ''I thank Mr. Previs for finally, if a bit belatedly, putting an end to this tragedy.''

The controversy began last April when the school superintendent, Carol Harrington, announced that an unusually high number of answers on the 1996 Iowa Tests of Basic Skills had been changed from incorrect to correct answers.

A State Department of Education investigation into whether Mr. Previs tampered with several years of answer sheets on the Connecticut Mastery Tests goes on. ''We are continuing our investigation and whatever agreement Mr. Previs reached with the school board does not preclude our revoking his teaching license if we determine he is guilty of misconduct,'' said Mark Stapleton, chief of legal affairs for the State Department of Education.

Several news organizations, including The Associated Press, have filed complaints with the Connecticut Freedom of Information Commission in an effort to make public both the terms of Mr. Previs's agreement with the school board and a report by private investigators that included interviews with school personnel, Mr. Previs and his wife.

While Mr. Previs and his lawyer, Howard Klebenoff of Hartford, have asked the school board to release the reports to them and the public, the board contended that its lawyers advised against releasing the information because of confidential personnel interviews.

Betty Sternberg, an Associate Commissioner of Education for the state, said that a state report has already concluded that tampering did occur at Stratfield on the 1993, '94 and '95 Mastery Tests and that ''while there is no direct evidence of the principal tampering with the test documents, the State Department of Education believes that his access to the test materials and his responses to inquiries leave us unable to exclude him.''

For the parents, there was disagreement over whether the matter had been resolved.

''No, I am personally not satisfied that everything has been answered or will ever be answered regarding this matter,'' said a spokeswoman for the P.T.A., Carol Sweeney. ''I accept that there was tampering -- but I feel very uncomfortable that we do not have a concrete resolution on who did it, and I want to know what really happened. Is the person who tampered still at the school? Will it happen again?''

Some parents, like Stacy Slane, said while they would like to have a more definitive resolution, they were prepared to put the issue to rest. ''I feel it's just time now to move ahead, to get back to concentrating on what is in the best interest of our children,'' Ms. Slane said.

Mr. Previs said that that was among his reasons for agreeing to a settlement. He said he resigned as part of an overall settlement to ''avoid costly and expensive legal proceedings for me and my family, which I believe would further disrupt the community.''

He also said the agreement was no admission of guilt. ''I still say, I know what I did or didn't do . . . and I didn't do it,'' said Mr. Previs. ''As I have continually stated, I could not tamper with the test and I do not know of anyone who tampered with the tests. Nevertheless, the cloud hanging over the Stratfield School, the staff and the students must be removed as soon as possible.''

While terms of the agreement were not disclosed, Mr. Klebenoff said Mr. Previs would receive full retirement benefits when he officially retires on July 1. He will remain on a paid suspension until that time.

Mr. Klebenoff also said he was not concerned about the state investigation that is continuing. ''They have nothing on Roger because he hasn't done anything,'' said Mr. Klebenoff, adding that his client would remain active in education in some as yet unspecified capacity.

The chairman of the Fairfield school board, John Madeo, echoed Mr. Previs's remarks in explaining why the school board agreed to the deal. ''The board agreed to the settlement to avoid the significant cost associated with pursuing termination proceedings against Mr. Previs,'' said Mr. Madeo. With the settlement, he said, ''the board believes that no further steps are required in order to put the test tampering matter behind us.''

A former Stamford principal, Jack Gilchrist, will be interim principal for the rest of the school year while the board looks for a permanent replacement for Mr. Previs.