A police spokesman, Comdr. Robert Gil, said he had no reason to doubt the authenticity of the tape and acknowledged that Chief Gates had been at the meeting longer than he had first recalled. Commander Gil said the Chief said today, "Well, it felt like five minutes."

One of the most compelling image of the riot was the savage beating of a truck driver that occurred between 6:30 and 7 P.M. Pacific time, about an hour before Mr. Gates spoke to the group. At one point, a woman said "We're behind you all the way and I want to see you as President of the United States." The group erupted in laughter and applause, and Mr. Gates said, "Thank you, and you're right." 'Remaining on Top Alert'

Some details from the audio tape were published today in The Los Angeles Times. The tape was recorded and made available by political opponents of Mr. Gates. Although he is to retire on June 28, there are many critics of the Chief who are seeking to limit any political future and influence he might have.

Details of the early hours of the riot began emerging today as the authorities ended four days of curfew in Los Angeles today as the schools, public libraries and banks reopened. But tensions remained palpable, and there was no move to reduce the presence of the police and heavily armed National Guard troops on the streets.

But despite the appearance of calm, the police and troops, cradling automatic weapons, maintained a high alert for the possibility of more trouble tonight. "We are remaining on top alert because we are not convinced it's over," Mr. Sheinbaum said. About 6,000 National Guard, Marine and Army troops were deployed on the streets, with 3,000 or so standing by in armories.

After several days during which many businesses were shut, office workers, shop clerks, lawyers and thousands of other employees filtered back into the city for the new workweek. In the surest sign of normality in Southern California, the freeways were again clogged this morning under hazy smoggy sky.

"Things are under control," said Mayor Tom Bradley on the fifth day after the acquittal of four white police officers in the beating of a black motorist, Rodney G. King, set off waves of killing, looting and arson in the nation's second-largest city. "As much as possible we want to return this city to normalcy. We want people to feel free, to feel secure."