A daylong hearing drew at least two dozen witnesses to the chambers of the D.C. City Council yesterday as a council committee reopened debate on controversial mandatory no-fault auto insurance and whether it should take effect in October.

The law, passed last year, was to go into effect April 1, but was postponed for six months after Mayor Marion Barry said his administration was not ready to enforce it.

Yesterday's hearing was on legislation introduced by council members John Ray (D-At Large) and Wilhelmina J. Rolark (D-Ward 8) that would eliminate the no-fault provisions of the insurance bill and put off mandatory insurance for up to three years while a commission studies the issue.

The major objection opponents have to no-fault is a provision that would prohibit lawsuits for "pain and suffering" damages except in cases that exceed $5,000 in medical costs or in cases of permanent disfigurement or death.

Washington attorney Harvey M. Katz, a no-fault opponent, told the Consumer and Regulatory Affairs Committee the law would "provoke the biggest run on doctors' offices in our history as accident victims do everything in their power to meet that $5,000 medical expense threshold."

A no-fault supporter, Grover E. Czech, regional vice president of the American Insurance Association, which represents about 165 companies, said efforts to repeal no-fault "cannot be considered reform legislation and . . . will prove to be considerably more costly for District consumers."