All the Lone Ranger needed was a mask, a horse named Silver and a trusty friend named Tonto. But last night's world premiere of "The Legend of the Lone Ranger" at the Kennedy Center was a pretty extravagent pow-wow. There was plenty of silver of a different sort, and a wealth of turquoise, too, lizard and ostrich cowboy boots and elaborately banded ten-gallon hats. It was a night on which you could revel as an urbane Indian or an oil-rich urban cowboy.

It was also a nonpartisan night: Sen. Strom and Nancy Thurmond showed up in a western shirt and jeans. Anne Armstrong, former ambassador to Great Britain, wore a white satin shirt and jeans. And Elliot Richardson opted for preppie western.

The film's co-producer, Jack Wrather, and his wife Bonita Granville Wrather flew 75 friends first-class from California for the two-day celebration.

Squash blossom necklaces and turquoise and Indian beads replaced the usual diamonds and rubies in the Madison Hotel vaults, according to assistant manager Mel Paull.

Even Lord Lew Grade, Wrather's co-producer, who had never worn western garb before, was decked out in a Stetson and western suit. His wife was in a fringed leather outfit made for the occasion by the London costumers Bermans. Grade thinks western clothes and films are popular because "they have heroes and the world is short of heroes at the moment. Without heroes, there is nothing."

It was strictly dressing up at last night's affair. Michael Horse, who plays Tonto in the film, wore a fringed suede suit that his girlfriend Willow Evans had spent two months bead-embroidering for him. And she was wearing $10,000 worth of gold and turquoise jewelry that he had made. "People love western clothes because within a basic pattern you can be more outrageous, and still have dignity," Horse said.

Very dignified was Lorena Nidorf, whose first husband was the late Louis B. Mayer, in a dance-hall gown by California designer Jean Louis. Martha Hyer Wallis was a pioneer lady in white dress carrying a shawl made from a patchwork crib quilt. Her husband, producer Hal Wallis, who put Reagan in such films as "Knute Rockne: All American," was wearing a double stand of silver nuggets and an antique sand-cast buckle. (At the party Thursday night, he told the president, "If I'd known how you were going to turn out, I'd have given you the Errol Flynn parts.")

Richard Stevens, head of the Wrather hotels, passed up the fullscale Indian headdress with his authentic chief's costume in favor of a medicine man variety complete with horns. "I'm probably the only fat, blond Danish Indian around," he said. "And now I know why the Indians lost a lot of the wars. Their clothes were too heavy."