THEIR JOB IS TO PROP UP NBC’S DAVID LETTERMAN

David Letterman’s writers thought it would be funny to have a shaving brush that looks like a celebrity. Kathleen Ankers had to figure out how to comb the bristles.

“This one will become Gene Shalit, once I figure out how to make a shaving brush’s hair like Gene Shalit’s head,” she said, demonstrating one of several jobs in development in her cluttered, closet-sized office at NBC headquarters.

There’s also a backup shaving brush, a Don King model, if the Shalit brush resists styling. “It’s not very flexible,” she complained.

Flexibility is the thing if you’re doing props for NBC’s “Late Night With David Letterman,” a job which Ankers shares with Jeremy Conway.

They make the giant chicken drumsticks, the maps made of meat, the gushing oil derrick on Jerry Lewis’ head, the harness for Zippy the Late-Night Monkeycam.

Sometimes they have just a couple of hours’ notice before taping begins at 5:30 p.m., and they’re often still at work at 9 or later.

They set up the “super slo-mo” bits, such as throwing eggs into a fan, and they test some of the stuff Dave drops from the five-story tower.

They worked up a Velcro suit to stick Letterman to a wall, a fizzing Alka-Seltzer suit and the giant suit o’ sponges that Letterman wore as he was dipped into a tank of water.

The worst, perhaps, was Dave’s dive into a vat of yogurt.

“Well, the yogurt one was so messy,” said Ankers, an energetic, Dr. Ruth-sized Britisher. “That was the cocktail dip where David went into a ton of yogurt--or almost a ton--wearing a suit with little pockets in it full of tortilla chips.”

After dipping, the dripping star headed up into the audience to offer chips around.

“Yogurt on the audience and the steps and so on,” Ankers said with consummate understatement, “is not usual.”

Next: the suit o’ magnets.

“There was some discussion of perhaps four burly housewives sticking David on a large refrigerator door as if he’s a refrigerator magnet,” Conway said.

“We will do most of the research on the magnets--what will be strong enough to hold David up to a surface--and we’ll work closely with the costume department in making that work.”

Head writer Steve O’Donnell has the sometimes risky job of testing the suits. The Alka-Seltzer suit released so much carbon dioxide that O’Donnell passed out, but adjustments were made to keep Letterman conscious.

Conway is rarely on stage, but Ankers is familiar to “Late Night” viewers as the daft librarian of the NBC Bookmobile. A natural comedian, she reads her lines for the bookmobile bits with the same deadpan aplomb she brings to her work.

Born in London, her backstage credits include costumes for “The Taming of the Shrew” for the Old Vic Theatre Co. in London, and set designs which nearly cover the history of NBC television, from “Omnibus” to “The Tonight Show” to Letterman’s short-lived morning show.

“Making straight props is one thing, but making props that enhance the joke is a little different,” Ankers said.

“You realize this is hard stuff to talk about, because it is essentially visual. It’s like Margot Fonteyn said: ‘If I could talk, I wouldn’t have to dance.’ ”