THE American theater is eyeing with more than the usual interest a play now in Broadway rehearsal. What's intriguing about ''Dancing in the End Zone'' is the cost-cutting way it is being staged: with concessions by management and the unions of theater employees, from actors to treasurers. Management is selling fewer than 500 of the theater's 700 seats, unionized employees are receiving lower wages, and there are fewer workers than union rules normally require.
All over the United States people involved in the legitimate theater, including many theatergoers, are asking serious questions about its viability. One of the gravest needs is to rein in the soaring costs of production and operation that have periled some regional theaters and darkened many large urban ones. In turn, the high ticket prices necessary for plays to break even have kept many middle-income people from attending plays.
Although Broadway is having a banner financial year on balance, many individual theaters are dark. Theaters in other communities are in similar difficulty.
To lower ticket prices, costs of producing and presenting a play - which can reach $1 million - must be reduced. Cost-trimming has halved the break-even point of ''Dancing in the End Zone''
The theater has a related problem: a paucity of first-rate scripts and playwrights. The theater underwent a similar dry spell in the early 1950s, only to bounce back as more playwrights with solid material emerged.
Today is different: Many potential playwrights are opting for the economic security of writing for television or the movies. Regional theaters that formerly sponsored them have had to present tried-and-true plays to retain solvency and are producing fewer new plays.
Yet the overall picture has positive aspects. More Americans saw theater performances in 1984 than in 1980. There is some sense that more Americans now would like to view live theater, to savor the electric interaction between performers and audience in a good play.
Corporate and individual support of live theaters is up, though government aid has tailed off.
Led by the Eugene O'Neill Center, regional workshops are playing a major role in developing new playwrights, offering the best an opportunity to hone their craft. Regional theater directors scout out new plays and playwrights at the workshops. Many aspiring playwrights remain willing to support themselves with part-time jobs while they struggle to succeed in the theater.
Thus some ingredients are in place for a theatrical revival. But for that to occur fully, costs must come down. Some connected with the industry believe its economic problems must deepen before major cost-cutting concessions will be made.
Others disagree, holding that improvement can begin soon. That is why the cost-trimming of ''Dancing in the End Zone'' attracts such attention. It may point the way.