By Steve Gorman

LOS ANGELES (Reuters) - Country-pop singer Shania Twain, teen star Britney Spears and R&B diva Whitney Houston are among the leading nominees for Monday's American Music Awards. But none will be performing on the show.

It's hard to say for certain what their individual reasons are, but it is a safe bet that if they were were to sing on the show, none would be welcome to perform on the granddaddy of music awards galas, the Grammys, next month.

Under an unwritten rule imposed by the National Academy of Recording Arts and Sciences, which sponsors the Grammys, a recording artist can appear on one show or the other, but not both.

``The fact of the matter is the (American Music Awards) show is four weeks away from our show, and we think it's our responsibility to our audience to give them a fresh look at performers,'' Grammys producer Ken Ehrlich said Friday.

``Offers that are made to performers (to appear on the shows) are probably made at about the same time, but it's up to the artists themselves to decide what show they would like to be on.

``I don't want to say its a policy. It's an understanding in the music industry that we all make the effort to keep these shows different. ... these shows are competitive.''

The producers of the American Music Awards disagree.

``It's a show that sells records. We don't see it as a competitive thing. We see it as something that benefits all who are involved,'' said Paul Shefrin, a spokesman for Dick Clark Productions Inc., which produces the AMA show. ``If you're preventing an artist from making an appearance, you're hurting that artist's sales.''

There's no question that entertainment awards shows of all stripes boost sales of the performers who appear on them, but the Grammys are by far the most prestigious and the most watched in the music industry.

Still, the 27th annual American Music Awards show has lined up such performers as teen singer Christina Aguilera, pop group 'N Sync, Latin crooner Enrique Iglesias, country duo Brooks & Dunn and rockers Lenny Kravitz, Beck and the Eurythmics. Pop vocalist Mariah Carey is scheduled to perform and to receive a special achievement award.

Spears, who landed three American Music Award nominations, will appear as a presenter on the show but will not perform, Shefrin said. Fellow three-way nominees Twain and Houston will not be present at the show.

One of the year's most celebrated talents, veteran rock guitarist Carlos Santana, will be in the audience as a nominee for two awards but will be absent from the stage.

Shefrin said he did not know whether particular artists had declined invitations to perform at the American Music Awards in order to remain eligible for a Grammy appearance.

In the case of Santana, whose self-titled band earned 10 Grammy nominations for its comeback album, ``Supernatural,'' Shefrin said, ``Let's face it, he's the centerpiece of their show.''

The performance lineup for the Grammys has not yet been announced. The three-hour AMA ceremony, to be hosted by comedian Norm Macdonald, will be aired live on ABC from the Shrine Auditorium.

Nominees are based on record sales and radio airplay, with winners picked by a poll of 20,000 American music buyers.

Reuters/Variety