DENVER — July 3, 1996 - 11:18 a.m. EDT

On a day with record-setting heat,a major power outage left 1.5 million customers in the western part of the country without electricity and phone service Tuesday.

The immediate results were traffic jams, lines to purchase gas and ice, stuck elevators and subway cars.

Many were stuck in office buildings without windows or air conditioning and others were threatened with the loss of all refrigerated and frozen goods. Hospitals and airports had to turn to emergency measures.

Several outages affected Oregon, Washington, California, Nevada, Colorado, Idaho, Utah, Wyoming, Arizona and the Canadian provinces of Alberta and British Columbia. The longest outage, in the Boise, Idaho area, lasted about two hours, yet the vulnerability of the interconnected system was made clear in that short time.

The outages occurred during heavy usage due to the heat wave, but utility officials weren't sure exactly what caused the outages. They plan to investigate today.

A utility spokesperson said linking the systems helps to conserve natural resources and keep costs down, but that a major problem can create a domino-effect throughout the system.

At the center of the outage were three 500-kilovolt transmission lines extending from dams in the Northwest down to the Southwest. All three lines, which can supply up to 2.2 million homes, were knocked out at one point. Authorities were unsure whether the lines caused the outages or were affected by a problem elsewhere.

Most hospitals and emergency services were able to switch to auxiliary power. Federal Aviation Administration officials in Seattle said air traffic controllers were able to use backup power generators. Elevators were knocked out for about two hours at the 19-story Ambassador East condominiums in Denver. Casinos in Reno briefly lost power. Las Vegas was unaffecte