THOSE EUPHONIOUS "Nineties" aside, 1991 really is the start of the new decade; and somehow the end of this one weighs more heavily. Without all that new-catchphrase hoopla, and without the exhilarating international upheavals that last year overshadowed the economic strains here at home, these closing weeks of 1990 seem strangely somber.

The retirement of the Slickee Boys may not be a political coup de gra~ce, but it is an emotional one, and in a way, a cultural one. When the band says the party had to end sometime, it strikes us that the party petered out a long time ago. The camaraderie, the adventurousness that characterized Washington nightlife 15 years ago when the Slickee Boys first formed has hardened: Performers are more competitive and critical, clubs are more "professional" in a sometimes exploitative way and audiences are more territorial and challenging in their adherences than in the years when Doctor Nightlife and all the young Dudes lingered in the balconies. A band like the Slickees, both sui generis and extravagantly synthetic (in both senses), would never be able to establish so diffuse and loyal an audience today.

What the Slickees invented always required a freight train of hyphens -- something like psychedelic-rockabilly-cyber-surf-garage-punk-new wave rock -- but the sound was so right, so paradoxically coherent that it became a kind of new-underground standard. Washington, so long celebrated (deservedly or not) for its alternative radio and non-commercial bands, learned "alternative" from the Slickee Boys. It also learned good humor, a lot of otherwise obscure tunes, the joys of head-shop nostalgia and the curiously stringent art of great pop music. It's hard to imagine any band, even the open-minded positive-force Fugazi, being so open-hearted.

It's also hard to imagine any group going through as many personnel changes (there have been 13 Slickees in all, counting the five current members) and remaining so close and so gleeful.

"I really love these guys," says frontman Mark Noone. "At the end of the night, we always kiss each other, and people don't understand why."

The Slickees cut more than 15 records, beginning with "Hot and Cool," said to have been the third new wave record ever released, and ending with the recent "Live at Last!"; but despite their European popularity, they somehow never rose out of the U.S. indie-label trap. Noone says the band came to a sense of conclusion almost a year ago ("actually, we talked about it every time we put out a new record -- 'if this one doesn't get it . . .' ") and settled the end-of-year dates several months back.

Their final performances, Friday and Saturday at the 9:30 club ($9; 202/393-0930), are expected to draw almost all former Slickees to the stage. (If anyone knows how to reach bassist-turned-rock critic-turned-record company flack Howard Wuelfing, tell him he's wanted.) Other alumni include Giles Cook, owner of Baltimore's appropriately righteous 8 X 10 club; Dynette Martha Hull, the one and only female Slickee; and founding rhythm guitarist and group conceptualist Kim Kane, who retired to his Date Bait band two years ago but remains, as Noone put it, "the group's guru, keeper of the philosophy."

The only original member left is lead guitarist Marshall Keith, whose underrated Dada-Ron Ron power drills always screwed the band together. Noone, whose ghoul-cool eyes and penchant for sharkskin jackets make him the Beetlejuice of rock 'n' roll, joined in 1978, but as the singer/manager is probably the most identifiable Boy.

With the demise of the Slickees (live, at least -- they have about 25 songs ready to record, if a good label makes them an offer), the band members are moving to another country, as it were. For one thing, their punkabilly alter egos, the Wanktones, will perform more regularly and less pseudonymously. Bassist Mike Maxwell and drummer Dan Palenski pursue the honky-tonk angle with the Capital Hillbillies; guitarists Keith and John Hansen have a '70s metal band called the Upsetters. Noone is producing (Grandsons of the Pioneers, Dogs Among the Bushes) and getting into more country with his wife, Ruth Logsdon of Plum Crazy.

And as for psycho-rock, well, the Slickees begat Date Bait, and Date Bait begat the Graverobbers and the Ubangis; and come spring, WHFS will be playing "When I Go to the Beach." But it won't help. Washington may not be as cool any more, but it'll be a lot colder.