District Mayor Marion Barry's administration yesterday opposed a city takeover of Antioch School of Law, saying the costs are too high.

Dwight Cropp, Barry's director of intergovernmental relations, testified at a hearing that the administration opposes legislation proposed by Hilda Mason (Statehood-At Large) to make Antioch a public law school.

He estimated that it would cost $9 million to $10 million to run the institution for 15 months.

Mason, who heads the council's Education Committee, is pushing to get her bill passed by the committee tomorrow. Council aides said the chance of committee passage is uncertain.

Antioch was created 14 years ago as a public interest law school with a mission of providing legal assistance to low-income persons and of training students to deal with legal issues that confront the poor.

But a series of problems has resulted in plans to close the school by 1988. The American Bar Association has threatened to remove Antioch's accreditation if it does not meet certain standards.

The school's parent university in Yellow Springs, Ohio, decided to withdraw its financial support of the law school. And an attempt to save the school by getting the University of the District of Columbia to take it over was rejected by UDC's trustees May 29, also because of the costs.

More than 80 witnesses -- including representatives of community groups and students and clients of Antioch -- signed up to testify at a hearing yesterday on the issue, most in support of the bill.

"Lord knows we have enough folks lawyers to serve the corporations," advocate for the homeless Mitch Snyder said in voicing his support for the bill. "But there is a distinct shortage of lawyers . . . who understand the needs of the poor."

Cropp said the $9 million to $10 million costs of acquiring the school and running it for 15 months would be met by only $3 million in tuition and other revenue. He said $6 million to $8 million would be needed to fund a permanent facility to meet the ABA's accreditation requirements.

But Tom Mack, dean of the Antioch law school, said the cost estimates quoted by Cropp were high. According to a council staff aide, Mack gave the committee an estimate of $2.8 million to run the school in fiscal 1987, which begins in October.

The school is not going to admitfirst-year law students in the fall, and even if Mason's legislation passes, could not admit them before early next year, the aide said.

"The budget is the key issue," the council aide said. The council had included $1.3 million in the fiscal 1987 budget for UDC's possible acquisition of the law school.

Cropp noted other options that had been discussed to provide legal studies to District residents, such as grants of $4,000 to $5,000 for residents willing to commit to a period of service to the D.C. government after graduation.

If Mason's bill is approved by the committee tomorrow, it could be considered only on a preliminary basis by the full council before its summer recess, which begins July 15.