CATHOLIC high schools in the five-county Philadelphia Archdiocese will be closed today, eight days after the lay teachers' union went on strike.

The Archdiocese said in a letter to parents of more than 16,500 students yesterday that all the opening tasks of the new year have been completed, but it couldn't "bring the entire school population back into the building with reduced staffs since this would compromise the safety of the school and our students."

Late afternoon yesterday, Rita Schwartz, president of the Association of Catholic Teachers, Local 1776, said that the Archdiocese had turned down a proposal from Patrick Eiding, president of the Philadelphia Council AFL-CIO, to have teachers return to the classrooms immediately while a mediator gets involved in the negotiations.

"They are unwilling to consider mediation and our teachers' return to the classroom," Schwartz said. "Unfortunately, this means that the schools will remain closed."

The Archdiocese maintained yesterday that a mediator isn't necessary.

"We believe we know our schools, our students, our parents and our teachers better than any outsider," said Theresa Ryan-Szott, chief negotiator for the Archdiocese.

Schwartz said that the 700 striking teachers were more worried about job security and the use of part-time teachers than salary increases. The lay teachers earn an average salary of $50,000 a year.

"It is a contract in which the Archdiocese wants to strip teachers of their right to job security," Schwartz said.

But archdiocesan officials said that they are seeking only to hire part-time teachers with certain expertise, for instance in engineering or foreign languages such as Mandarin or Farsi.

"We're not reducing our full-time teachers," said Mary E. Rochford, superintendent of Catholic Education.

"We are trying to see what we can do to make a school program more exciting for students."

Although Schwartz has said that the contract isn't about money, the Archdiocese noted that the union has asked for a salary increase of 14.5 percent over three years.

The Archdiocese's proposal is 7.84 percent over the same period.

"We want to give our teachers all we can give them, but we are a tuition-based system," Rochford said.

"As salaries go up, the tuition goes up. As the tuition goes up, students and families are not able to afford it."

The strike does not affect Catholic parish schools for children in grades K-8.