A security guard was arrested Wednesday on suspicion of torching the historic Universal Studios backlot where Warren Beatty flirted with Madonna in "Dick Tracy" and a city square featured in "Back to the Future Part II."

Michael J. Huston, 40, of Tujunga was booked for investigation of arson and held in lieu of $20,000 bail in the multimillion-dollar fire, said Deputy Rich Erickson of the Los Angeles County Sheriff's Department."He was on duty when the fire started and after questioning he was arrested early today at the studio," the deputy said. "We won't disclose a possible motive."

Huston is an employee of Burns International Security Services, which is under contract by Universal. He had been on the job one month, said Dan Slusser, general manager of Universal City Studios.

The John Landis movie "Oscar," a production of the Walt Disney Co. and starring actor Sylvester Stallone, was the only film shooting on the backlot at the time of the fire, said Slusser.

Hundreds of firefighters backed by water-dropping helicopters put out the windblown flames about three hours after the fire broke out at the 420-acre studio, Hollywood's biggest and longest-running movie factory. Universal Studios is visited by millions of tourists each year.

Most of the damage was to the sunbaked wooden facades along the route of the studio tour, the third most popular tourist attraction in the nation.

"A lot of the streets are pretty well destroyed and are going to have to be rebuilt," Bennett said.

Among outdoor sets destroyed were New York Street, where parts of "The Sting" were filmed, Brownstone Street, and Courthouse Square, where Michael J. Fox rode his jet-powered skateboard in "Back to the Future Part II." The "Dick Tracy" set also was gutted, county fire inspector Jim Gandee said.

But it was "business as usual" Wednesday with the first tour tram leaving on schedule at 9:30 a.m., said studio publicist Joan Bullard. She said about 20 percent of the 420-acre property was burned and estimated damage in the hundreds of millions of dollars.

"We are extremely disappointed to have lost history," Bullard said.

But she said only one "attraction," or amusement-parklike feature of the tour, was damaged - King Kong. "The mechanical part of that works, but there was water damage and we are checking the structural integrity of the building," Bullard said.

However, fire officials said the earthquake ride also was damaged.

The cause of the fire was not immediately known. One firefighter was slightly injured.

Studio executives toured the $630 million theme park Wednesday to assess the damage.

The flames, fanned by winds gusting up to 50 mph, were doused as they crept up to two film vaults. The Universal film library, which includes "E.T. The Extra-Terrestrial," "Jaws" and "Twins," is worth hundreds of millions.

The film library is vital to acquisition talks between Matsushita Electrical Industrial Co. and MCA Inc., Universal's parent. Matsushita has been discussing a multibillion-dollar buyout of MCA for several months.

The studio nestled in the Hollywood Hills 10 miles from downtown Los Angeles features a seven-hour journey through the backlot and includes a guided tram tour that takes viewers into sets and a simulated earthquake.