When it comes to designers, Broadway producers do not believe in spreading the work around.

Donald Holder, Brian MacDevitt and Kenneth Posner did the lighting for almost a third of the 38 shows that opened this season.

A mere four designers — Jess Goldstein, Michael Krass, William Ivey Long and Catherine Zuber — came up with the costumes for nearly half the 2004-05 productions.

Goldstein, who tops the current threads list with five shows, says Broadway was always thus. “When I started in the business, everything was designed by four ladies,” he says, referring to Theoni V. Aldredge, Willa Kim, Florence Klotz, and Jane Greenwood, who designed two shows in 2004-05: “Who’s Afraid of Virginia Woolf?” and “On Golden Pond.”

How do such achievers get it done? Why are they on overdrive?

“You have shows on your schedule a year in advance,” says Zuber, “and then you are surprised.” Pleasantly, in this costumer’s case: “Little Women” and “The Light in the Piazza” came together in New York sooner than she expected, and “Doubt” made the transfer to Broadway. Suddenly, like it or not, Zuber was an overachiever.

The same thing happened to Long.

“This spring, I thought I’d put some things to bed,” he says. Wrong. For instance, Robert Goulet’s last-minute entry into “La Cage” required new costumes; the band uniforms in “Sweet Charity” needed redoing; and over at the Steiner Studios, Mel Brooks wanted the chorus girls in the “I Want to Be a Producer” number to be encased in pearls, not gold as they are in the Broadway version of “The Producers.” Amid such activity, “A Streetcar Named Desire” opened right on sked. “My first Tennessee Williams,” notes Long.

When lighting struck this Broadway season, MacDevitt and Holder were there for five shows each.

“I feel like I’ve been in tech since Labor Day,” says MacDevitt, who also lit “The Color Purple” in Atlanta over the holiday. It eased his workload a bit that, among the musicals “Pacific Overtures,” “Good Vibrations” and “Sweet Charity,” he lit two plays, “The Pillowman” and “‘Night, Mother.” “I would never do four musicals in a season. You can do three plays in the time it takes to do a musical.”

The fact Broadway often resembles a very small town eases the load, too. “In a funny way, it wasn’t that difficult because all mine were in New York this season,” says Goldstein. “Try designing in Seattle; San Diego; Washington, D.C.; and L.A. in one season. That’s hard.”

Goldstein’s shows — “Julius Caesar,” “Brooklyn Boy,” “Sight Unseen” and “Good Vibrations” — were all midtown projects. “Suddenly, doing ‘The Rivals’ up at Lincoln Center felt like another state,” he says.

Set designers aren’t so prone to multicredits, but then the lifting is heavier per show. John Lee Beatty and Robert Brill clocked in with three plays apiece. Scott Pask had it even busier with one play and two tuners. “It helped that my shows (‘La Cage,’ ‘Pillowman’ and ‘Sweet Charity’) were all on West 45th Street,” says Pask.

David Rockwell had two credits, “All Shook Up” and “Dirty Rotten Scoundrels,” but each was a big $10 million-plus tuner. And they arrived back to back in March. And the Elvis Presley show switched theaters. “There was enough backstage space at the Marquis to store the units, but at the Palace much of the scenery has to be chain-hoisted up,” says Rockwell, who had to redesign late in the game.

In addition, the designer had two other midtown projects this spring. His Rockwell Group put the finishing touches on the new restaurants Bar Americain and Nobu 57th Street.

In the designer sweepstakes, Holder probably holds the overachiever title. Listing his 2004-05 credits (“La Cage,” “Gem of the Ocean,” “All Shook Up,” “Streetcar”), he forgets “After the Fall.”

“That was this season?” he asks.

In addition, he made his Met Opera debut with “The Magic Flute,” and out of town there was August Wilson’s “Radio Days” and “She Loves Me” at the Guthrie, which is why he couldn’t make the preem of “Streetcar.” “My family was there, but I was in Minneapolis,” says Holder.