THE CORN doesn't just grow high in the San Francisco Mime Troupe's "Eating It." The bio-engineered super-corn grows high fast - very fast. It not only resists herbicides, it cannibalizes neighboring plants and replaces them. Devised to combat world hunger, it's a world-wide environmental nightmare leaving a legacy of "dark acid clouds raining mutant genes on the seared flesh of Mother Earth."

Just in time for its annual Fourth of July performance in Dolores Park, the San Francisco Mime Troupe is back with its 38th annual free summer show. In keeping with its traditions, it's delivered yet another snappy musical drama in the public interest, laced with sharp comedy, bright original tunes and expertly performed caricatures. The topic this time is one of the most pressing, fast developing and complicated - and, for many people, scariest - on the international scene: genetic engineering, and the market forces working fundamental alterations in the food we eat.

The collaboratively developed script only skims the surface of some of the issues involved, and still needed work as of Saturday's opening performance in Dolores Park. But "Eating It" has the makings of one of the company's stronger and more entertainingly provocative outings as the troupe hones its material. Even in its current form, it inspired a standing ovation from a substantial portion of the six or seven hundred in attendance - an unusually small opening day audience for the Mime Troupe, on a windy and cool July afternoon.

It also marks something of a transition. Though partly shaped and polished by Joan Holden, who's listed as dramaturg, "Eating It" is Holden's last show as a member of the collective. After a remarkable 32-year run as the troupe's principal playwright, Holden quietly announced her retirement last week to devote more time to other projects. She will not be easy to replace, either for longevity or sustained quality.

Primary writing credits this time out are shared by Michael Gene Sullivan, who plays a lead role, longtime

troupe songwriter Bruce Barthol and Ellen Callas, with songs by musical co-directors Barthol and Jason Sherbundy. What they've put together is a semi-sci-fi political fable in a fairly classic Holden mode.

Smartly staged by veteran Mime Troupe director Dan Chumley on a stage full of ingenious trap doors (a cleverly cartoonish set by Melpomene Katakalos with wonderfully caricatured costumes by Huy K. Tran), it begins in the year 2178. The mustard-colored skies have become so polluted by the lethal bacteria in genetically altered pollen that humans have to live in sterile bubbles. Aged Dr. Isaac Albright (Sullivan), overwhelmed by guilt for his part in creating this ecological catastrophe back in our own time (he gets regular "life-extender shots" administered by Keiko Shimosato's comical robot Phalox), invents a time machine to go back and try to set things right.

That takes us to the present, when Isaac is a wheeler-dealer young scientist playing for very high stakes with the charmingly smarmy drug and agribusiness tycoon Bob Murtaugh (the risibly amoral Ed Holmes), head of the Bobco conglomerate. Isaac is making big deals for a super-corn being developed by his aptly named wife Synthia (the brilliant Velina Brown), deals that involve big bucks for Bobco and Albright Laboritories as well as the presidential aspirations of Governor Jay Witherspoon II (Amos Glick), a none-too-bright son of a former president with a Texas accent.

A mock TV commercial, featuring a plaintively clueless Victor Toman as a starving Latin American peasant child, frames the debate. Bobco's reckless push for greater profits through genetically engineered (and patented) food is being sold as a People Against Starving Children campaign. A dynamic song battle between Synthia and her mentor, Dr. Esperanza (a vibrant Shimosato), poses the issues in terms of the need for greater agricultural yields versus unforeseen ecological and health threats - and freedom of scientific inquiry ("Can't she see? I am Galileo and she's the Church" Synthia sings to Esperanza's "The servant of science, so righteous and noble, should take a stroll around Chernobyl").

Meanwhile there are anti-Frankenfood demonstrations in the streets, young Isaac is subverting his wife's careful testing programs to protect the bottom line, the wonderfully kinetic corn stalks are turning vicious and the aged Isaac is wandering among the demonstrators with amnesia. As the story moves toward its cliff-hanger conclusion, other aspects of the problem are outlined in dialogue and the delightfully catchy, eclectic songs.

Sullivan, whose old and young Isaac engagingly hold the show to

gether, is superb wooing the doubtful Synthia back to work in the science-for-the-people "Our Dream." Brown and Shimosato argue the "Servant of Science" complexities in with vibrant resonance and Brown wraps up the show with a dynamic Weill-ian "Short Term Gain." Toman and Glick, as Canadian farmers Fred and Al Berta, outline the economic ravages of the patented seed scam in a loping Woody Guthrie-ish "Savin' Seeds." Holmes brilliantly delineates Bobco's tactics in a hilarious "5 D's" ("Deny, delay, dupe, dump and divide").

The politics are clear, with some pointed material on international finance creating famine by replacing subsistence farming with monocultural export crops. (Left unconsidered are the pressures of overpopulation on food resources and the environmental degradation caused by many traditional agricultural practices.) But some of this is told or argued rather than effectively dramatized, at the expense of some leaden patches of dialogue - a problem that could be quickly addressed with a few rewrites.

Even as it is, "Eating It" is a nutritious entertainment - short (65 minutes), timely, funny, provocative, sharply staged and beautifully performed. It just goes to show the continual wonders of splicing hot political issues with the unique skills of the San Francisco Mime Troupe.