By Jill Serjeant

LOS ANGELES (Reuters) - At what may be the height of her early career, teen sensation Taylor Swift finds herself facing the downside of stardom -- naysayers.

The 19-year-old pop/country singer-songwriter heads in to Sunday's American Music Awards with a leading six nominations after a dream year of sold out concerts and the best-selling album in the United States.

Swift will compete Sunday against the late Michael Jackson for artist of the year, and is nominated for favorite female artist in the pop/rock, country and adult contemporary categories, along with favorite album for "Fearless".

But her higher profile, including becoming the youngest person to win the Country Music Association Entertainer of the Year award, has left her open to recent sniping by some music lovers who complain about her voice in live performances.

Just three years after releasing her first single, the pop/country singer-songwriter has struck an emotional chord with millions of fans for heart-felt songs like "Fifteen" and "You Belong With Me" about first loves, being an outsider and the perils of high school.

"I can't think of anyone else (in pop) music who inspires the level of passion in their fans on the scale she does right now," said Rob Brunner, music editor of Entertainment Weekly.

Still, that view is not shared by all and in recent weeks, her detractors seem to have raised their level of criticism just as Swift has seen her star soar into the stratosphere.

"Wobbly" and "embarrassingly weak" are some of the comments -- many from disgruntled fans of traditional country music -- found on web sites after recent live performances, including on television show "Saturday Night Live."

"I think the songs are great, the records are great. But she doesn't have the pipes," said Bob Lefsetz, a former music industry executive and author of The Lefsetz Letter blog.

NO TOPPLING TAYLOR

The negative chatter has done nothing to dissuade fans from snapping up tickets to Swift's recently extended concert tour. Nor has it curtailed sales of "Fearless" -- the biggest selling U.S. album of 2009 with 2.1 million copies, and No. 3 in 2008.

And many industry watchers question the importance of technical ability in an era where Britney Spears can happily lip-synch her way around the world during her "Circus" tour, and where the vocal pitch correcting device, Auto-Tune, is widely used in recording studios and at concerts.

Swift, who plays guitar and piano, never lip-synchs. As for Auto-Tune: "I have never used Auto-Tune in a live television performance, and I have never used Auto-Tune in any of my concerts. That is a promise," she said in a statement to Reuters.

She has performed live for more than one million people and won a slew of awards voted on by fans and the industry. If her singing is occasionally off-key, that's what makes her genuine and is what she brings to the music arena, her managers say.

"(Taylor) tries to hold herself to a better standard but perfection is not one of them. At 19-years-old, I don't know how she deals with the nerves (of singing live). And sound issues are not always in our control," Robert Allen, one of Swift's managers, told Reuters.

Lefsetz agrees with music critics that Swift "is phenomenal live". But he added: "I think it is a sad state of affairs when one of the biggest artists in the world can't sing."

Brunner said comments like that are missing the point.

"I don't listen to pop music to hear people hitting the note but because it connects with me in some profound emotional way. While it may not be a Celine Dion or Barbra Streisand voice, whatever she's got is something that people are really connecting to," he said.

Swift will not be at the AMA's on Sunday because she is on tour in England ahead of going to Australia in February.

(Editing by Bob Tourtellotte)