Clay Aiken — of American Idol fame — appears on stage as Sir Robin in Monty Python’s Spamalot at the Shubert Theatre in New York. In recent weeks, closings have been announced for Spamalot, Spring Awakening, Xanadu, and Legally Blonde.

AP / Joan Marcus

At the new, high-tech TKTS booth in Manhattan’s Father Duffy Square recently, flashing red LEDs were hawking half-price orchestra seats for Monty Python’s Spamalot, The Phantom of the Opera and 22 other Broadway shows.

With the U.S. economy in tatters and neither investors nor ticket buyers rushing to part with cash, Broadway producers are seeing red: Hit shows are playing to half-filled houses while investment capital for all but the safest bets is drying up.

“It’s been tough even for shows where there were investors already lined up,” said Margo Lion, 64, the lead producer of Hairspray, which will close on Jan. 4 after a six-year run. Early fall is always brutal at Broadway box offices, as summer tourists leave and local patrons wait for the critics’ yeas or nays on new shows. In recent weeks, closings have also been announced for Spamalot, Spring Awakening, Xanadu, and Legally Blonde.

The producers of A Tale of Two Cities closed the show Nov. 16 after struggling for two money-losing months. It lost its entire $16 million capitalization.

Sales for last year’s Tony Award-winning best play, August: Osage County, were down 27 percent from the week before, according to figures recorded by the Broadway League, the commercial theater’s trade organization. Numbers like that are causing investors to pull back. After all, Broadway is an industry where 80 percent of new shows fail in the best of times.

“I have nothing in the pipeline and it’s a very happy state to be in,” said Roger Berlind, 78, a founding partner of investment firm Carter, Berlind & Weill (later Shearson Loeb Rhoades) and, since 1976, one of Broadway’s most prolific producers. He has put his resources behind serious works like Tom Stoppard’s Rock ’n’ Roll as well as lighter fare such as revivals of Guys and Dolls and Kiss Me, Kate.

As a director of Lehman Brothers Holdings Inc. since 1985, Berlind was also an inside witness to the debacle taking place further down Broadway, on Wall Street. He declines to discuss that subject.

“We’re all impacted by the economy,” Berlind said. Adam Epstein, a co-producer of Hairspray, abandoned plans for a $4.5 million revival of Godspell when a key investor pulled out.

“The harsh truth,” said producer John Breglio, 62, “is that the statistics will be very sobering and there will be a lot of empty theaters in January. It’s going to be a very tough road in terms of big, expensive new shows. No one’s jumping in, taking risks.”

A retired partner in the law firm of Paul, Weiss, Rifkind, Wharton & Garrison LLP, Breglio turned producer to mount the profit-making revival of A Chorus Line that closed in August. He is now working on a revival of Dreamgirls scheduled to open in Seoul in February before eventually coming to Broadway.

The South Korean production is fully capitalized at $5 million, he said, or about one-third of the cost on Broadway, where his only additional expense will be the hiring of an American cast.

“Our health on Broadway is much more reflective of what happens with tourism than anything else,” Breglio said. “The mega-hits will survive, but if international tourism goes down, we have a much more serious problem.”

Several new musicals are likely to be affected by that forecast, including Billy Elliot, with music by Sir Elton John, previewing at the Imperial; Shrek, which began previews two weeks ago at the Broadway Theatre; and a revival of West Side Story that has begun advertising heavily and is scheduled to begin previews at the end of February at the Palace. Shrek is promoting deeply discounted tickets available through January.

Even as producers struggle to bring costs down, working on Broadway continues to be an expensive roll of the dice, as the novice producers of Tale of Two Cities most recently learned. Spider-Man, a new musical staged by Lion King director Julie Taymor, is in development at a reported cost of $40 million. It features a score by Bono and the Edge, from the Irish rock band U2.

Shows like Spider-Man and Shrek are, to use the favored jargon of the moment, “branded” and stand a better chance at getting capitalized than more obscure titles, said Frederick M. Zollo, 55, a film and theatrical producer with a record of backing risky projects.

Zollo, however, isn’t in a hurry to bring his version of an independent movie to Broadway; he expects to see other projects arrive more quickly in such impecunious times. He and a group of co-investors have created a $5 million pool to seed new productions.

“The legitimate theater had problems during the Depression, but film business was rock ’em-sock ’em,” Zollo said. “I think we’re going to have real problems now. But just as the studios had to make better movies to stay alive during those years, we have to make better theater.”