They call themselves "tribute bands." Their critics call them "clone bands," or even "necrophiliacs."

They're performers who play the part of someone else, from the quartet that sang in "Beatlemania" on Broadway to the Elvis impersonator down at the local roadhouse.

Such acts most often impersonate dead musicians (Presley, John Lennon, Jimi Hendrix, Jim Morrison). But they also take on the living -- bands that have broken up (Creedence Clearwater Revival, the Who) and even intact bands that don't tour often enough to satisfy their fans (the Rolling Stones, Bruce Springsteen and the E Street Band).

They get precious little respect, but rock 'n' roll impersonators are doing good business from coast to coast, especially in out-of-the-way towns: For example, the Back Doors, one of the most popular "tribute bands," regularly sells out 1,000-seat clubs all over North America. Saturday night, the group will join two other bands -- Fire, playing the Jimi Hendrix Experience, and the Revival, playing Creedence Clearwater Revival -- for the "Concert That Never Happened" at the Warner Theatre.

In some cases, tribute bands have been reviled by associates of the musicians they impersonate. But some have been heartily endorsed by people close to their subjects: Morrison's sister, Anne Morrison-Graham, for example, has publicly praised the Back Doors.

"Some people say it's wrong to bring these groups back to life," says Jim Hakim, leader of the Back Doors. "But what about the great plays from Shakespeare? They're still being done and not by the original artists. It's like Richard Burton playing Alexander the Great: Everybody knows that Richard Burton is just an actor and not a Greek general, but people can still enjoy the way he brings that character back to life."

Hakim bears only a passing resemblance to Morrison, the Doors' lead singer; he relies heavily on his voice, mannerisms and costume to create the impression. Decked out in black leather pants and jacket, Hakim spouts Morrison's poetry between songs and leads the crowd in chants, much as the late singer once did.

"So many newspapers have misquoted me, saying that I believe I am Jim Morrison," Hakim complains. "That's nonsense; I know who I am offstage like any actor would, and I like who I am.

"I do think I understand Morrison better than anyone I've ever met. I spent all my time, 24 hours a day, seven days a week, thinking about this guy for two years before I put this band together. I got my hands on everything possible -- film clips, concert tapes, interview tapes, books, articles -- I even talked to people who knew him."

Charlie Hennebaul, the leader of the Revival, places less emphasis on visually imitating John Fogerty, leader of Creedence Clearwater Revival. "They never had a strong visual identity," admits Hennebaul. "We do wear flannel shirts, but mainly we just go out and try to play Creedence as well as we can. We're pretty much note perfect."

Hakim, who estimates he played in 40 rock bands between 1963 and when he quit the music business in 1972, hatched the idea of the Back Doors five years ago, after he had drifted back to his home town, Wilkes-Barre, Pa.

"I knew I wanted to get back to rock 'n' roll," the singer recalls, "but I didn't want to do another Top 40 band, another living jukebox. I wanted to take it a little further; I wanted to bring back the Doors 100 percent -- not just the songs, but the whole persona and stage show, because that's where the mystique came from."

Hakim hired three friends from Pennsylvania and took the Back Doors on the road; they were an immediate success. One day when he was back home, he told Hennebaul that he sounded a lot like Fogerty and ought to consider forming a "tribute band." Hakim put his fellow Wilkes-Barre native in touch with the Back Doors' agents, Stage Productions of Rockville.

Ironically, neither Hakim nor Hennebaul had ever seen his subject in person; both had to rely entirely on film clips and records. Hennebaul's hastily assembled quintet made its public debut at the Wax Museum in Washington. By the third song the group had the crowd singing along to "Who'll Stop the Rain?"

"No matter how many times I play 'Bad Moon Rising,' I still get a thrill out of it," says Hennebaul. "I don't really feel frustrated. Does an actor feel bad because he's doing the same play every night that another actor did 20 years ago?"

Many of the musicians in tribute bands harbor frustrated ambitions; most of them have demo tapes in their back pockets. But it's even harder to slip original songs into a "tribute" show than it is into a Top 40 set.

"My long-range ambitions are to record my own songs," acknowledges Hakim, "and to have hit records, just like the Doors would if they were still around. Playing in a tribute band is a lot better than being in a Top 40 band, but it's still not the ultimate, which is being yourself.

"We can never be as good as the originals, because we're not the originals; they were the creators, and we are the imitators. This is the best I can do right now, but it's not the ultimate goal anyone should have if they want to be a true musician or a true artist. Eventually you have to move on to something else."