Three months into 2000 and the mainstream music trends for a new decade are emerging already. All classic genres (hard rock, heavy metal, bubblegum pop and on and on) have been worn down to the bone, which leaves only remixing the old to make something fresh. Currently in the music industry's bag of (successful) tricks: sports metal, generic power-punk and gorgeous plasticine teenagers who either have done time as Mouseketeers or should have.

Out of these three options, No Doubt [ tickets ] has chosen the middle road for its new album, ''Return of Saturn,'' due in stores on April 11. Unfortunately for the band, its first live gig ''in, like, a year-and-a-half,'' according to pink-haired front woman Gwen Stefani, does not bode well for upcoming album sales.

Showcasing five new numbers at an invite-only gig at London's Hanover Grand nightclub on Monday night, No Doubt did not reassure fans of its staying power. Instead, it proved with the songs ''Ex-Girlfriend'' and ''Staring Problem'' that it has descended into the artless, scratchy-guitars, screechy-vocals, pop-punk territory of Republica and old Sneaker Pimps. Although the band got the audience bouncing--and the 600-strong crowd shouted lyrics back to a black-clad Gwen during the 1995 classic hit ''Just A Girl''--the two new songs were a disappointment.

Nor was Stefani's voice suited to the slower new tunes ''Marry Me'' and ''Magic's In The Make Up''. Macy Gray, or even Skin from Skunk Anansi, would have done a better job with those songs. Stefani strained as she tried to go against her attractively brazen nature. Both songs seemed to lack the ''classic'' No Doubt ska element that was heard in ''Don't Speak'' and ''Spider Webs,'' which the band also played. The reggae-influenced backbeats in ''Marry'' and ''Magic'' were watery at best. The low point of the night, however, was the new tune ''Simple Kinda Life,'' which was devoid of any spark. Because it was so tame, however, this was the only breather the audience got throughout the otherwise fast-paced set.

Despite the lack of ingenuity in the new material, No Doubt was energetic as always, and Stefani was the perfect entertainer, working the crowd in a way that can only be rivaled by ex-Take That member and UK pop hunk Robbie Williams. Like Monday night's crowd of exceedingly peppy teenagers, the hordes of fans across America, who have already ensured that the group's upcoming tour is a sell-out, will walk away from the live experience on a serious emotional high. The album experience, however, will most likely be a once-told tale: stored right next to ''Tragic Kingdom'', but passed over time and again for the more exciting old favorites.