A federal appeals court, overturning a lower court's decision, said yesterday the head of a Woodbridge church school exceeded his constitutional rights in expelling two white sisters because he thought one of them had a black boy-friend.

The unamimous decision by a three-judge panel of the 4th U.S. Circuit Court of Appeals in Richmond also delivered a sharp rebuke to 78-year-old U.S. District Judge Oren R. Lewise of Alexandria, saying that his earlier finding had been both "erroneous" and "vague" in parts. It ordered him to hold hearings on a $70,000 damage claim by the girls, Melissa and Charlotte Fiedler, against the Marumsco Christian School, which has since filed for bankruptcy but is still operating.

"This is a stunning victory," said Leonard Rubenstein, president of the Virginia American Civil Liberties Union and cocounsel for the Fiedler family. "[The school] was claiming falsely that religious freedom was involved, but it was really plain, old, secular gardenvariety racism."

Lewis last year had agreed with Aleck Lee Bledsoe, the 38-year-old principal of the school, that he had a constitutional right to forbid interracial dating at the school under constitutional guarantees of religious freedom.

Yesterday's appeals court ruling said, however, there was no evidence to support Bledsoe's assertion that interracial dating violated the tenets of the Marumsco Baptist Church.

"Noting other than Bledsoe's own conclusions indicates that his conviction regarding interracial romantic relationships is shared by the institution or that it is, in any event, more than a 'personal preference,"' the opinion said. "The district court's contary finding, offered without benefit of factual analysis, is not supportable by any interpretation of the evidence offered at trial."

The appeals court said it had examined the church writings, its bylaws and statements of faith, and found they "do not address the subject of interracial romantic relations nor do they mention race relations at all."

Instead, the court said, the church had a history of fostering interracial friendships, and had done nothing to discourage an interracial marriage in the family of a church deacon.

Bledsoe expelled Melissa Fiedler, then 14, early in 1979 after he had seen her in the company of Rufus Bostic III, a black classmate. Her 11-year-old sister Charlotte was later expelled when the girl's father, Raymond Fiedler, threatened Bledsoe with a lawsuit.

Bledsoe, who had testified in court that the Bible contains several references to God's opposition to interracial dating, yesterday declined to comment on the appeals court decision or on whether he plans to appeal.

"We're still tied into the case, and there's a lot of money involved," he said. "I really don't think I should talk about it just yet."

Bledsoe's Marumsco Baptist Church, which once claimed over 200 members, has now shrunk to about half of its former size as chruchgoers fled the controversy. About half the school's 165 pupils have also been withdrawn since the squabble began, according to Bledsoe.

Raymond Fielder, who moved his family from their home in Manassas to an undisclosed location after a series of harassing phone calls and letters, refused yesterday to return a reporter's telephone calls to him at a work site in Valdosta, Ga.