Richard "Cheech" Marin and Thomas Chong are "Still Smokin' " --that's even the name of their latest film venture--but the daffy fires that often lit their four previous films are in danger of extinction. Or,to put it in terms they and their fans surely will understand, it's down to seeds and stems.

In previous films, the Chicano-Chinese comedy team always managed to dress up old routines with frilly and silly plot devices. They came across as the amiable Laurel and Hardy of the Vietnam-era counterculture. But as that culture recedes, jokes about drugs (mostly pot), hippies and the confusion when the former is ingested by the latter seem archaic.

Plot-wise, "Still Smokin' " is the pits, with Cheech and Chong reduced to playing themselves. They are among dozens of Hollywood celebrities invited to a Burt Reynolds-Dolly Parton film festival in Amsterdam (funny, heh!). They also are the only ones to show up--the festival is as short on funds as the film is on laughs. So the boys decide to do a benefit concert, which gives them an excuse to reenact old routines. These include two dogs running into each other on the corner, drag queens in outer space, a dope-a-thon, blues legend Blind Melon Chitlin' and other assorted characters and scenarios.

"Still Smokin' " labors its points in low style, with the two comedians occupying 95 percent of the dialogue and screen time. This is simply a badly disguised concert film. The photography is abysmal, the dialogue often garbled, the transitions incredibly awkward, particularly a number of fantasy sequences. The whole thing was shot with a European crew in Amsterdam, which ought to sue for underrepresentation. The humor is persistently sophomoric (shots of wild animals copulating during Cheech's encounter with the Scandinavian hotel maid).

On the theory that their audience is hooked on humor--even bad humor--Cheech and Chong are plunging ahead with two more features, "Yellowbeard" and "The Corsican Brothers." Maybe they'll come up with some of the good old stuff, but this feeble effort implies a bit too much of the dealer's ego, the kind that holds that occasionally you may be short on product, but you'll never run out of dopes to buy it. STILL SMOKIN'

Directed by Thomas Chong; written by Thomas Chong and Richard (Cheech) Marin; director of photography, Harvey Harrison; art director, Ruud Van Dijk; edited by David Ramirez and James Coblentz; music by George S. Clinton; produced by Peter MacGregor-Scott for Paramount Pictures. This film is rated R. THE CAST Cheech....Cheech Marin Chong....Thomas Chong Promoter....Hans Van In't Veld Hotel Manager....Carol Van Herwijen Assistant Manager....Shireen Strooker