The D.C. City Council yesterday approved a six-month delay in the city's mandatory no-fault auto insurance law, acting on an emergency request from Mayor Marion Barry.

The measure originally was scheduled to go into effect April 1, but Barry told the council his administration could not implement regulations governing rates under the new law in time for consumers to make informed choices before buying insurance. In addition, Barry contended that some proposed rates were too high.

In order to approve the delay, the council first had to declare an emergency, which it did by a 9-to-4 roll-call vote--the minimum two-thirds majority required. That action was the key vote taken yesterday. The council then approved the actual delay, which means the law will not take effect until Oct. 1, by a voice vote.

Some supporters of no-fault said in the wake of yesterday's action that they were worried they might not be able to protect the measure against an anticipated attempt to scuttle it. Council member John Ray (D-At Large) has already promised to lead an effort to kill the measure.

Those who spoke in support of the delay yesterday said they were merely trying to avoid chaos that might result if motorists were prohibited from renewing their auto tags on April 1 if they could not prove they had insurance, as required by the new law.

Officials have said that about 100,000, or 40 percent, of the private vehicles registered in the District are currently uninsured.

Council member Polly Shackleton (D-Ward 3), who voted against the delay, called the council's action "a national disgrace" because of the number of uninsured drivers here. "I'm outraged that all of you in the Barry administration who had a responsibility to act failed to do so," she said.

The council acted yesterday in less than two hours and for the most part without the kind of rhetoric and rancor that surfaced during a five-hour committee session on the bill last Friday and that plagued the council last summer when it passed the original bill.

"The mayor has admitted the executive branch has not prepared as well as it could have," said Council Chairman David A. Clarke, who voted to declare the emergency that allowed the delay. Regardless of whatever political reasons Barry had, Clarke said, "certainly the executive branch has failed."

Opponents of the delay argued that the Barry administration sabotaged the law, which was passed last July, by purposely failing to prepare for its implementation, and that the administration overstated rate increases.

Barry has denied such allegations. Annette Samuels, his press secretary, said yesterday that Barry supports the concept of no-fault and would have vetoed any effort yesterday to kill the measure outright. However, Barry has not committed himself to maintaining the current no-fault law, Samuels said.

The law was passed only after an unprecedented lobbying war between insurance executives, who favored the law, and trial attorneys, who opposed the bill's limitations on the right to sue for damages.

Insurance representatives and some consumer groups have argued that no-fault legislation would lower personal injury insurance costs by eliminating most lawsuits. The no-fault law, however, would not cover property damage to automobiles.

Ray suggested yesterday that the council appoint an independent commission to study the issue of mandatory insurance and its effect on the poor. "If not, the discussion will always end up about the insurance companies versus the trial lawyers," he said.

During yesterday's vote, representatives of the trial lawyers, who had attended previous meetings in large numbers, were absent. Insurance lobbyists sat quietly as the law they had fought for was delayed.

Voting for the delay were Clarke, Ray, Frank Smith (D-Ward 1), John A. Wilson (D-Ward 2), Charlene Drew Jarvis (D-Ward 4), William R. Spaulding (D-Ward 5), H.R. Crawford (D-Ward 7), Wilhelmina J. Rolark (D-Ward 8) and Jerry A. Moore (R-At Large).

Opposing the delay were Shackleton, Nadine P. Winter (D-Ward 6), Betty Ann Kane (D-At Large) and Hilda Mason (Statehood-At Large).