FORT WORTH — It was about the classiest lounge act you could ever hope to see.Vocalist Steve Lippia saluted the voice and memory of Frank Sinatra in all his Rat Pack glory at Bass Hall on Tuesday night with the Fort Worth Symphony Orchestra.Instead of being surrounded by slot machines and knee-breakers, Lippia conjured the Vegas of the past amid violins and revelers wanting to see in the New Year in a quiet, retro kind of way. But that was fitting because Lippia, who has performed at Bass Hall twice before, is a class act. He has a genuine passion for his subject — Old Blue Eyes — and the music Sinatra sang, which permeates everything he does on stage. And he works well with a truly big band.Lippia’s set included a number of Sinatra favorites ( A Very Good Year, I’ve Got You Under My Skin, The Way You Look Tonight, That’s Life, Strangers in the Night, The Lady is a Tramp) and just a few surprises. One of the best in that latter category was an excellent rendering of Stephen Sondheim’s Send in the Clowns with only piano accompaniment. That arrangement offered a chance to hear Lippia’s voice more purely and cleanly, and it was an impressive experience.On the whole, Lippia sounded a great deal like Sinatra without sounding exactly like him. He did not have Sinatra’s phrasing, because no one does. But he offered an eerily similar tone and was especially good at ending a lyric or phrase in exactly the way Sinatra would have. The orchestra, conducted by Steve Sigmund, had a mixed evening. Everyone played well, but some played more than others. The string section appeared a bit bored, but they added a glossy sheen to the numbers that required them. The poor wind section was left to their own devices for most of the concert and were almost pitiable for their inactivity. But the brass section had the night of its life, joining the big band rhythm section that was added to the orchestra to make the tunes swing.Lippia, who makes his home in Las Vegas, was also a genial host for the packed house of about 2,000. We learned that, before settling on singing as a career, Lippia attended law school (which he hated), was a stock broker and worked in the construction business.But, fortunately for us, he could not give up the stage. So, thanks to Lippia and the Symphony, Vegas came to us this New Year’s Eve, instead of the other way around.