A proposal by American University to move its law school from the main campus to the former site of the Immaculata Preparatory School on Tenley Circle dominated a D.C. zoning board hearing yesterday as homeowners and community groups opposed the plan.

During the hearing before the Board of Zoning Adjustment, which started in mid-morning and went into the evening, community leaders said that the law school's seven-day-a-week, 8 a.m. to midnight schedule would bring more traffic, noise and parking problems to their quiet neighborhood.

"If they came up with another use that doesn't create objectionable conditions then it's no problem," said Charles Knauss, a spokesman for Neighbors Opposed to American University.

"They concluded they wanted AU Law School here and that it wouldn't be objectionable, but they should have done it the other way around . . . , " Knauss said.

The university purchased the 8.2-acre property at Wisconsin and Nebraska avenues NW late last year from the Sisters of Providence, an order of Catholic nuns who ran the prestigious girls' high school for almost 80 years. The sale price was $7.6 million.

The order said the sale, which upset students and parents at the school, was necessary to provide funds for the retirement and medical care of its aging members.

Donald Myers, the university's vice president for finance and treasurer, denied that the law school would harm the community. "Law students are typically older and more academically oriented than other students," he said. "We felt this type of student body would be compatible with the neighborhood," Myers said.

He said the university and the community were still trying to resolve their differences. "There are only a few points left that we don't see eye to eye on," he said.

He added that the university hoped the proposed move of the law school would provide a "distinct identity" for its 1,100 students and 150 staff and faculty members, but refused to change the school's hours.

Under the university's plan, one of the property's five buildings would be used as a dormitory for 150 law school students. Settlement and transfer of the property, located about a mile from the university's campus at Nebraska and Massachusetts avenues NW, is scheduled to take place shortly after Immaculata closes in June 1986.