Ann P. Kahn, a seven-year veteran of the Fairfax County School Board, was elected chairman of that policy making body last night by unanimous vote for her fellow board members.

Kahn, 54, who represents the Providence District, cast one of the three dissenting votes last winter when the board decided to allow a high school graduation to go on as scheduled despite opposition from two Jewish Students.

That vote came after sisters Lynn and Susan Stein honor students at W.T. Woodson High School, objected that commencement exercises were scheduled for the Jewish sabbath. The rejection of the Steins' request for rescheduling was one of the board's most controversial decisions of the past year.

Kahn's election as board chairman does not necessarily signal a future shift in policy governing graduation schedules, but several Fairfax County Jewish leaders said yesterday they would regard her election as an encouraging sign. The board is still under pressure from these leaders to revise the policy.

Kahn did not address the question during her brief remarks following her election in which she praised her predecesors for setting high standards" for the office.

She replaces Rodney F. Page, who resigned from the board last month, saying he wanted to devote more time to his law practice and family.

The change in the 10-member board's leadership comes during a period of rapid transition that has seen three members deport in a single week last month. The resignations were due in part to the board's decision to close seven elementary schools. That politically unpopular move cost two members -- Ruth H. Dell and Robert Smith -- their seats when members of the County Board of Supervisors indicated they would not be reappointed.

Also elected without opposition last night was Board Vice Chairman Roger Teller, 48, an asociate professor of mathematics at Georgetown University.