First Interstate Bank opened a seminar last week on how to respond to a major disaster with an unscheduled mini-disaster.

The start of the bank's two-day conference at a Newport Beach, Calif., hotel was delayed 30 minutes by a predawn power failure that left the hotel and much of the surrounding area without electricity.Many business executives who had arrived at the hotel Sunday overslept when the alarms in their rooms did not go off. Once awakened, they faced cold showers because the hotel's water heaters are electric.

The inconveniences and delay were minor, particularly compared with the disaster - and subsequent Herculean efforts to resume business at the bank months ago - that motivated the seminar.

Last May 4, a fire severely damaged several floors of First Interstate's 62-story headquarters building in downtown Los Angeles. A worker was killed and vital functions at California's fourth-largest bank were disrupted.

Less than three weeks before the fire, First Interstate had conducted a trial run of its emergency plan for resuming critical bank business in the event of a disaster. The rehearsal scenario had envisioned an earthquake, but the fire put the system to the test.

By accounts from within the bank and outside experts, the system worked with remarkable smoothness. In fact, the plan has become something of a hallmark in the growing field of disaster preparedness for major businesses.

Experts were so eager to learn from the First Interstate experience that the bank was inundated with calls for advice in the weeks after the fire. Demand became so heavy - and the explanations so complex - that the bank decided to offer an intensive seminar to share its experience, said John Y. Popovich, director of public affairs for the bank.

The bank expected mild interest and was surprised by the overwhelming response. More than 280 people paid $735 a person to attend the seminar. The attendance list read like a Who's Who among major U.S. corporations - Atlantic Richfield, B.F. Goodrich, Boeing, Chevron, Hewlett Packard, Kaiser Permanente, Lockheed, Merrill Lynch, Paramount Pictures, TRW, Wells Fargo Bank, and the purveyors of Monday's interrupted electricity, Southern California Edison.

"Take a look at what happened in that fire - that speaks to why we're all here," said Lawrence M. Kalmis, vice president in charge of contingency planning for Chemical Bank of New York. "We're here to see what we're doing well and what we might be doing better."

Colen H. Emerson, the First Interstate executive in charge of the business recovery plan, opened the seminar by cautioning the audience not to underestimate the complexity of managing a crisis.

To drive home the point, he outlined a few of the seemingly mundane tasks accomplished in the hours after the fire: 1,000 critical employees were relocated in a matter of hours; 3,000 telephone numbers were redirected from the devastated headquarters to the emergency site seven blocks away; a system was set up to distribute 128,000 pieces of mail a day; more than 800 new telephones were installed in two days; and an entire new securities trading floor, with 160 computers and work stations, was created in four days.