For such a robust, often low-down form of comedy, farce is a remarkably delicate mechanism.

When everything clicks, it gathers speed like an avalanche, burying you in laughter. But put the doors in the wrong place, drag out the timing or allow the characters to turn superficial, and the mechanism goes klunk.

At Saint Vincent, which employs a solid group of (largely Pittsburgh) pros, farce is usually in good hands. And Ken Ludwig, playwright of its current "Leading Ladies," is pretty dependable himself, as his popular "Lend Me a Tenor" testifies.

		'Leading Ladies' Where: Saint Vincent Theater, Saint Vincent College campus, Route 30, Unity Township. When: Through July 21; Tues.-Sat. 8:10 p.m. Tickets: $7-$16.50; 724-537-8900.

But the result, although far from just a klunk, is equally far from a comic avalanche. The Saint Vincent company must accept some of the responsibility, but Ludwig is also to blame, although I'll know that better if I get to see some of the other productions planned this season, notably at the Mountain Playhouse in Jennerstown.

The chief Saint Vincent merrymakers are Michael Fuller and David Cabot as Leo and Jack, two English actors of limited success who find themselves adrift in the Elk, Moose and VFW show-biz wasteland of eastern Pennsylvania and adopt a farfetched scheme to feather their nests. This is, in short (but there's nothing short about how slowly Ludwig establishes his premise), to masquerade as sisters in search of a sizable inheritance.

If that sounds familiar, it is somewhat like the scam played by the Duke and the Dauphin in "Huckleberry Finn," with the difference that Twain's con men are both livelier and more despicable. Ludwig's are basically nice guys who fall in love with the play's matching comics, young women played by Renata Marino and Stephanie Burden.

It's nice to have a happy ending to root for, but it does rather blunt the comedy. A buttinsky doctor played with precise timing by Joe Warik contributes some nicely acid comic lines, as does Patricia Reilly, the surprisingly feisty source of the expected legacy. (Ludwig knows crankiness can be funny; would there were more of it.) The chief villain is played limply by Richard Sautter.

To be fair, that villain is also limply written, with no real edge. Along with taking far too long, Ludwig lets the play sag safely toward the middle, instead of generating the greater and greater leaps of absurdity of which inspired farce is capable. Director Joe Reilly can't save it from this shortcoming.

Still, Fuller is the perfect actor for Leo, able to infuse even a caddish scheme with genuine charm, and Cabot, with his basso profundo voice, is a fitting counterweight -- and he looks especially funny in a dress.

Marino has some comic chops, too, but she never makes real sense of her oddly naive character, and costumer Margaret Gilfillan has togged her out in improbable garb. Burden, though, is a constant joy, able to take the eccentricity and shrewd-stupidity with which Ludwig has blessed her and milk every comic possibility.

As any farce should, "Leading Ladies" gets funnier near the end, in spite of a pause for a pointless dance sequence. It's the start that seems so slow.