Groundlings at 20: Deft Turns at Laughter : ‘Good & Twenty’ review opens with a sound problem that demonstrates their smooth professionalism.

Last week’s 20th birthday party for the Groundlings focused primarily on the company’s alumni. But it wasn’t just a homecoming. The weekend opening of the troupe’s latest revue, “Groundlings Good & Twenty,” proved that the current model remains a lean, mean comedy machine.

The reviewed performance began with an announcement from director Deanna Oliver that the sound system was broken, so the opening sketch, “Boogie Nights,” would be skipped. No problem. The unlisted substitute, “Caution,” was, well, a caution--a disaster movie spoof in which a group of office workers confronted a deadly wet floor, with pitch-perfect performances by writers Jim Jackman and Cheri Oteri, plus Phil LaMarr and John Cervenka.

This ability to reach into a bag of tricks and come up with something that’s just as funny as the already announced sketches is a testament to the depth of this Groundlings team and its sense of smooth professionalism.

Of course, this Groundlings outing may have seemed especially sharp because Oliver restricted the always risky group improv to one set early in the program--and that one set, a quick charades game among four disparate brothers, was as funny as most of the 19 rehearsed sketches. It also helped that the sound system was quickly fixed so that the two-man band of Willie Etra and Teddy Zambetti, and the company’s sound effects, got to show off after all.

So did the Groundlings themselves. It was quite a night for Jennifer Joyce, shifting with precision from a distressed Kathie Lee Gifford, to a woman repulsed by her date’s (Tim Bagley’s) odd laugh, to a teen-ager impatient with her annoying “Grandma Strawberry,” to a weary rural mom, to a disgruntled bra purchaser. But then most of the others executed similarly deft turns, if not quite as many of them. Karen Maruyama, for example, transformed from “Grandma Strawberry” into Judge Lance Ito doing a stand-up routine.

Several other sketches also addressed local subjects, and Mike Hitchcock wrote or co-wrote the most successful: a conversation with Steve Kehela about the relative merits of Westwood and the Valley, and a crisp musical satire of CityWalk, sung to the tune of “Camelot.” The biggest visual gag of the evening came in the appearances of Mary Scheer and Jim Wise as Faye Dunaway and Andrew Lloyd Webber on their day in court.

Bagley and LaMarr did a sharp bit about a middle-aged man who wants to be a homeboy, Oteri and Cervenka were a charming pair of freeway ramp dwellers and directions mavens, and Michael McDonald demonstrated enough quick wit as a fake talk show host to inspire the hope that he might someday do it for real. A few less stellar sketches were at least short.

* “Groundlings Good & Twenty,” Groundling Theatre, 7307 Melrose Ave., Fridays, 8 p.m.; Saturdays, 8 and 10 p.m. Runs indefinitely. $17.50. (213) 934-9700. Running time: 2 hours.