As flames leapt across the stucco-and-foam-coated crown of the 32-story resort, the Monte Carlo, firefighters mounted the roof and suppressed the blaze in a little more than an hour.

The cause of the fire is under investigation, but the Clark County fire chief, Steven M. Smith, said welders working on the roof might have played a role in it. The top of the building is where much of its air-conditioning machinery and other electrical equipment are situated.

The blaze closed the Monte Carlo, which has some 3,000 rooms and a 90,000-square-foot casino that had operated continuously since the resort opened in June 1996 with a theme of stately European-style elegance. The Monte Carlo has been a middle-of-the-market option in the shadow of its more opulent, more expensive neighbor, the Bellagio.

Thousands of guests were evacuated to the arena of the MGM Grand, a second property of the Monte Carlo's parent company, MGM Mirage, to be offered accommodations at other company resorts, including the Bellagio and New York-New York.

It is unclear when they will be able to return to their rooms at the Monte Carlo to retrieve their belongings, said a spokesman for MGM Mirage, Alan M. Feldman. The resort will remain shut, Mr. Feldman said, until county building inspectors can assess it and determine which areas can reopen when.

Mr. Feldman said he thought the two top floors of rooms and suites were occupied when the fire broke out. A warning system alerted the staff to evacuate the guests, he said. He did not have an estimate as to how much the shutdown would cost the company, but did say, "We have a lot of work ahead of us."

It has been a little more than 27 years since 84 people were killed in a fire at the old MGM Grand, about a half-mile north of the Monte Carlo. Among the nation's deadliest hotel blazes, that one remains second only to the Winecoff Hotel fire of 1946, which killed 119 people in Atlanta. The MGM Grand fire led to far stricter fire safety standards for the hotel industry here, and some experts credited them for Friday's orderly evacuation and few injuries, all minor.

"The lessons of that incident clearly came into play in this fire," said David G. Schwartz, director of the Gaming Studies Research Center at the University of Nevada, Las Vegas.

Meredith Frankel, 60, has lived for more than 30 years in a subdivision less than two miles east of the Strip and, until the construction of newer resorts, could see the Monte Carlo from her porch.

"I can't tell you how chilling it was to see the smoke and hear those sirens," she said of Friday's fire. "I thought, 'Here we go again.' But then it turned out O.K. I'm amazed."