The past year has been a good one artistically for Arena Stage, but an undercurrent of financial uncertainty about the future plagues the organization despite each new cultural milestone.

The city's resident theater, at 6th and Maine streets SW, is celebrating its 30th anniversary to the accolades of theater critics, civic leaders and art-lovers throughout the area. Ticket sales for the three theaters contained within Arena Stage have remained in the 90 percent-plus bracket. And the current season, featuring Bertolt Brecht's "Galileo" is a virtual sellout.

Almost drowned out by these positive events, however, is the faint sound of an alarm bell. According to executive director Thomas Fichandler, Arena Stage faces severe financial difficulties within the next couple of years unless the nonprofit organization can find and develop new sources of revenue.

"The important thing," Fichandler said recently, "is that Arena Stage has been an extraordinarily successful organization over the years. We're not crying 'Wolf!' yet, but we need to alert the local business community now about our future need."

That need, quite simply, is cash.

Arena Stage operates under the corporate name of the Washington Drama Society on an annual budget of just under $3 million. Of that total, about $2 million is raised each year through ticket sales. That leaves an operating deficit this year of about $907,000. And that just happens to be the target amount Fichandler and Elspeth M. Udvarhelyi, the director of development at Arena, hope to raise from private sources this year.

Fichandler cites inflation as the primary culprit in the theater's struggle for fiscal balance.

"Inflation has shot expenses way up," he said. "We're a highly labor-intensive industry, with little opportunity to increase productivity."

Another problem is the "uniqueness of Washington," according to Fichandler.

"Unlike other major cities, there are very few sponsoring corporations. Also, there is no viable state government to approach for funds," he said, admitting that the federal city could provide only very limited funding due to its current financial status.

Local businesses contributed only 1.35 percent of the funds required by the theater last year. This problem is one of recognition.

"There's still out there a misconception of an organization like the Arena Stage," said Udvarhelyi. "We are a major District employer [150 employes] and we really do a great dealfor the city. We're saying not enough people recognize what we're doing. Local business does not perceive the importance of the arts to the community."

Fichandler and Udvarhelyi have charted an agressive fund-raising drive to help meet the deficit. Direct-mail appeals recently were sent to 175,000 selected area residents and the response, according to Udvarhelyi, has been good.

"We keep a very clean list," she said. "It's updated every six weeks, or so."

In addition to direct-mail soliciting, Fichandler and Udvarhelyi have been approaching various corporations and foundations, as well as local businessmen. But the resources of final resort remain the local and federal government.

"The trends in philanthropic giving tend to show corporations taking over in support of nonprofit groups," said Udvarhelyi. "Business is realizing it must take over some of the expenses of providing these arts."

Arena Stage owns outright the building it presently occupies and owns half the land. The other half is rented from the D.C. Redevelopment Land Agency. Arena Stage has until 1986 to buy that half of the property, and needs about $125,000 for that purchase. The alternative is a 99-year lease.

"We're in no immediate danger but in two or three years we might very well be," Fichandler said. "It is very urgent that the Washington business community take a look at their obligations to the cultural life of the city."