T.C. Williams High School sophomore Kathleen Murphy surprised the Alexandria City Council yesterday with a polite but aggressive pitch that a student be given a seat--and a vote--on the city's nine-member school board.

"Students have a right to have a say," said Murphy, 15, who brought along a petition supporting her effort that was signed by 640 of the 2,500 students who attend T.C. Williams, the city's only high school. "We see things being decided for us," argued Murphy, who said students do not have a voice in such things as curricula and school operating hours.

What Murphy got for her effort was a council promise to study the request and a 15-minute lecture from Carlyle C. Ring Jr., council member and former school board chairman, on how adults know what is best.

"Young people do have a lot of good ideas that can be put into the process," Ring told Murphy as she stood before the council. "But it is very difficult for students to project what you are going to need." Ring told Murphy that a voting student member on the school board raises a fundamental philosophical question about whether a student has the foresight to make a decision based on the "right reason."

Other members of the council, including Mayor Charles E. Beatley Jr., weren't particularly opposed to having a student on the board, but were sharply against giving that student a vote.

Council member Patricia S. Ticer pointed out to Murphy that Beatley is a non-voting member of the Washington Metropolitan Area Transit Authority, but nevertheless has a considerable effect on that board's decisions.

Murphy was not swayed. "A student without a vote cannot get anything actually done for the students," said Murphy, who founded the Committee for Student Rights and Representatives at T.C. Williams last January.

Murphy, who lives on West Braddock Road, said she is not interested in the board position for herself. She explained that her task is to clear the way so a "devoted, dedicated" student could do the job.

Councilman Donald C. Casey suggested, and the council agreed, that its staff explore the matter.

In a telephone interview later yesterday, Judith Feaver, vice chairman of the Alexandria School Board, said she has serious reservations about making a student a voting member of the board.

"I would only support a non-voting student member of the board," Feaver said. "I know a lot of students are not going to like this, but no student has the maturity to make the decisions day after day that a school board must."