zpswat December, Ampersand : 1979 ; Willie was like working with your favorite shoe, " Redford says, comfortable, durable and spe cial. Any man who can ad lib a line on camera like Tm gonna get me a bottle of tequila, one of them Keno girls who can suck the chrome off a trailer hitch, and kick back' deserves to be in movies, " writing songs or in jail. BY KATHERINE ORLOFF J he Inca is a combination res taurant, bar and casino about one mile in distance and sixteen light years in ambience from the Las Vegas Strip. The house El g collection, calls themband, a selves the Salt Lick Outlaws. With a solid rhythm section and the harmonized vocals of the leader, J.J ., and his blond wife, Darby, they're as fine a house band as an American bargoer could wish for. Tonight the El Inca is packed with Unisemi-ragta- ISP I VV" " f As versity of Nevada students, local cowboys, and a large contingent of movie people, including director Sydney Pollack, who leads a cheering section of actors, production staffers and technicians. The smoke is dense and there is an air of expectation when J.J. quiets the room at the end of the first set. "Ladies and gentlemen," intones the bandleader, "the best there is in country music, and our good friend Willie Nelson." The audience picks up the phrase and it becomes almost a chant, until Nelson gets on stage and down to business. Two long sets later, after the crowd has had enough tequila and St. Pauli Girl beer to float the QE2, Nelson, 46, is both tired and jubilant, his audience excited and drunk, and the cool, rainy Las Vegas night suffuses the room with fresh air. Nelson is in Las Vegas to make his first motion picture, The Electric Horseman. The film, directed by Pollack, stars Nelson's pal Robert" Redford and recent Oscar-winner