"PLEASE REMAIN seated while we play the national anthem," intoned a voice from the band. A thousand or so local patriots, gathered in Dolores Park on a sun-drenched Sunday afternoon, did just that as the San Francisco Mime Troupe band sidled into an odd, speedy kazoo-and-trumpet-laced version of "The Star-Spangled Banner."

Then came the blessing from two blissed-out members of the Sisters of Perpetual Indulgence. And then came "City for Sale," 85 minutes of hard-hitting and often hilarious satire in the signature style of the nation's oldest radical, activist theatrical troupe.

It was, if not the Bay Area's most hallowed, then certainly one of its most beloved Fourth of July traditions: The opening of the Mime Troupe's summer season of free shows in the parks. It also marked the company's 40th year since its founding in 1959 as the R.G. Davis Mime Troupe (an anniversary that will be celebrated with panels and a performance retrospective at the Cowell Theater and Palace of Fine Arts in December).

In keeping with its history, the troupe is marking its 4Oth by taking on yet another hot, divisive issue: The loss of low-income housing and small-business space to urban gentrification in the form of so-called live-work lofts. It isn't, however, giving the subject a treatment that lives up to its own best standards.

"City for Sale" is enjoyable. It's good, basic agitprop theater that should help rally the troops to the development moratorium cause. It's clear, very funny and performed with sharp, comic zest. But only at times. It's also a bit simplistic, underdeveloped in construction and theme, and uneven in staging and performance.

That's partly because the Mime Troupe is missing some of its more reliable practitioners of its form of fast-paced comedy and broad, but sharply etched, caricatures this summer. Popular favorites Ed Holmes and Michael Gene Sullivan are on leave, and Keiko Shimosato is trying her hand at directing rather than performing this year. Shimosato succeeds better at creating sharply timed comic moments than at building momentum between scenes or lacing them with inventive sight gags.

The set, by Donyale Werle, is an attractive street-scene cartoon, but without the comic versatility of the troupe's usual designs. The chief problem, though, seems to be with the script itself, written by veteran Mime Troupe playwright Joan Holden and Kate Chumley (her daughter with the company's usual director, Dan Chumley). As widespread as the gentrification problem is, "City" treats it in San Francisco-centric terms that feel a bit insular even to someone from just across one of the bridges.

Agnes (newcomer Stephanie Taylor as a well-meaning but gullible innocent), a "techno-serf," newly arrived in the area, is suckered into buying into a live-work loft development. In a very SF touch, Agnes protests that she's not an artist (a reference to the 1988 city ordinance authorizing conversions of live-in work spaces for artists in industrial zones). Rapacious developer Ben (Amos Glick) tells her she's a software artist and that the residents are planning to move anyway.

That's not how the denizens of the targeted building see it, of course. They include Alonso (Luis Oropeza) and his auto body shop, and a group of musicians. Daria (Velina Brown), the vocalist, thinks development is the natural order of things and opts to split. Xavier (Victor Toman), the songwriter, is a local determined to fight the insidious yuppie threat. Junior (longtime Mime Troupe songwriter Bruce Barthol) is a stoned-out old hippie bassist relying on Ben's father's promise that he could always live there.

Junior, Xavier and their neighbors take their problem to the mayor, Lavinia (Brown), an African American populist-elitist contradiction who seems to have a lot in common with a well-known local politician ( "I wanted to be the people's mayor, but then the parties started and I forgot" ). She's up for reelection and sinking in the polls because of broken promises to solve the homeless and mass transit crises (she also has a problem with pie throwers).

Lavinia espouses their cause, seeing it as a win-win situation (everybody hates yuppies, right?), until her savvy assistant (Oropeza) reminds her that the developers are major contributors - and Ben starts to blackmail her. The situation is promising, but Holden and Chumley haven't developed it beyond positing characters and their complications.

Fortunately, the songs - by Barthol and keyboardist Jason Sherbundy - are upbeat rock and samba delights, beautifully delivered by Brown, Barthol, Toman, Oropeza and Taylor. The band is hot, with some bright trumpet riffs by Marina Garza. And some of the performances are outstanding.

Longtime troupe fave Brown is hilarious in her slick smooth-tough shifts as the mayor and in exploiting the comedy of her well-padded dress (clever costumes by Huy K. Tran). Versatile Teatro Campesino veteran Oropeza is a delight in the sheer energy and sharp definition of his caricatures, while Barthol plays his confused old hippie with perfect comedic timing.

Glick is deftly comic as an oddball artist and an ominous street poet, but his Ben lacks the degrees of insidious malevolence of a good Mime Troupe villain. Toman is a solid performer, but his Xavier feels underwritten. More importantly, so does Agnes, despite Taylor's engaging performance. The typical clueless character who comes to her senses, she undergoes her change of heart offstage.

But then, none of the characters in this "City" holds the stage long enough or develops enough for us to identify with them. As funny as it is - Holden has lost none of her skill in crafting sharp satirical quips - and as deftly as it explains its theme, "City" doesn't manage to give its issue a human face.