Southern Rock Enshrined, but Still Raucous Allman Brothers at the Beacon Theater ANN POWERS 03/09/99 When a rock band signs up to do 18 concerts in one place in one month, it had better be able to show off more than one personality. The Allman Brothers, repeating last year's residency at the Beacon Theater in Manhattan, manage that trick with ease. Here are a few things the Allmans are in 1999. The Allman Brothers are legends. The group remained elegantly absorbed in its playing throughout Friday's long performance. The guitarist Dickey Betts, in a cowboy hat and multiple tattoos, rogueishly embodied Southern rock. The heft of middle age made Gregg Allman seem more soulful as he played Hammond organ and sang his rough blues. Behind these icons, mementos spanning the band's career flashed on a big screen: concert posters, album covers, portraits of the group's deceased members, Duane Allman and Berry Oakley. These Rock-and-Roll Hall of Fame inductees had brought along their own museum. The Allman Brothers are also a cult band. Friday's show included rarely performed chestnuts like "Revival" and the group's version of "Stormy Monday." Fans screamed in delight at these treats as the most devoted scribbled down set lists. Many were college-age followers of the recent generation of jam bands, pleased to see the new Allman Brothers bassist, Oteil Burbridge, who also plays with the popular Aquarium Rescue Unit. The group attracts these young acolytes because they emphasize improvisation. Songs stretched elastically as members took protracted solos. A new tune by Mr. Betts, "J. J.'s Alley," shifted from a be-bop-inspired beginning to Santana-style rock to Texas blues. The drummers Jai Johanny Johanson and Butch Trucks got their chance to jam on the instrumental "Les Brers in A Minor," which had Mr. Trucks pounding two bass drums in double time. But the Allman Brothers are a well-oiled machine, too. The Southern boogie the group invented, which mixes blues with jazz and soul, relies on a fast, danceable beat. The way most songs circled back to almost irritatingly catchy riffs got a bit tedious in Friday's third hour, but the band's stamina barely flagged. Some would say the Allman Brothers are the soul of classic rock: music men unswayed by trends who have perfected a fusion of the genre's main ingredients. Traditionalist innovators and liberal good old boys, they are multifarious and contradictory. So is classic rock. In that way, the band is true to form. The Allman Brothers are to play at the Beacon through March 27.