A far-reaching study, conducted over the past 18 months, says that new theaters in downtown Washington are not only desirable but economically feasible.

The report, to be released today at a press conference at the National Theatre, calls for the inclusion of small and mid-sized theaters in future office buildings, identifies 14 possible sites and suggests tax and zoning incentives that could facilitate their construction.

Mayor Marion Barry will attend today's press conference along with city developers and representatives of the arts community. The mayor declined comment yesterday, but is expected to make a policy statement regarding the arts.

"It's an extraordinary, timely report. We are at the right moment in the development of the city for this to happen," said architect David Schwarz, whose firm, David M. Schwarz Architectural Services, helped prepare the study in collaboration with the League of Washington Theatres and the District of Columbia Office of Planning. "But if it is not done now, it will never be done. In five years, all the available sites will be built."

Noting the dramatic expansion of small and mid-sized theater companies over the past decade, the report points out that "the shortage of viable performing space . . . [is] the single biggest problem facing the performing arts in Washington today." Eight of the 11 member theaters of the league are currently engaged in a search for new quarters or will be in the near future.

Some (Horizons and the Woolly Mammoth theater companies) are housed in churches; others (Studio and Source theaters) occupy rented commercial spaces that seat 100 spectators or fewer. Another, the Paradise Island Express, leads a largely itinerant existence. Escalating real estate prices, soaring rents and the lack of large, industrial buildings that could be transformed into theaters have exacerbated their plight.

"Most of these second-generation companies are ready to move on and up," said Howard Shalwitz, artistic director of the Woolly Mammoth and one of the authors of the report. "That means having control over their performing space."

The study points out, however, that the costs of including a theatrical facility in a new building would result in a rent seven to eight times more than a theater company could afford. The developer, it suggests, must therefore be offered compensating incentives by the District government.

A 150-seat theater, for example, would have an annual market rental value of $336,847. But, the report says, it would be unrealistic to expect a theater company to pay more than $44,000, leaving a difference of $292,847. In the case of a 500-seat theater, the figures increase dramatically. Its annual market rental value would be $1,306,175, but the mid-sized company that could effectively occupy the space would be hard pressed to pay more than $175,000.

To close the gap between development costs and a theater's budget, the study proposes:

*Rear-yard waivers, which would allow a builder to use a larger portion of a given lot than currently permitted under D.C. zoning regulations in order to compensate for the space taken up by a theater.

*F.A.R. (floor area ratio) bonuses, which would increase the allowable amount of rentable space in a building to offset the loss of space to a theater.

*Real estate tax reductions for projects incorporating a theater.

*A tax on entertainment-related activities, such as restaurants and movies, to help support theaters.

*Special municipal bonds to reduce the effective interest rates for financing projects containing theaters, thereby decreasing a developer's costs.

*Tax-exempt industrial revenue bonds, issued by developers, working in concert with the city, for projects including theaters.

*The formation of a nonprofit trust, which could receive a tax-deductible contribution of performance space from a developer, and then, in turn, rent that space to a theater company at below-market rates.

*The creation of a city agency to buy space that it would rent to theater companies.

While conceding that no single approach would work on its own, the report suggests that a combination of some or all of them could alleviate the space crunch.

"Obviously, the theaters can't do it by themselves," said Shalwitz. "City governments don't give away performing space. And developers are in the business of making money. That's a fact. The bottom line is that they all have to come together in a three-way partnership."

Several small theater groups are already located on 14th Street NW, a corridor viewed by some as a potential theater district. The report, however, sees the development of the downtown area as a preferable alternative. Ford's Theatre, the National Theatre and the Warner Theatre already bring sizable nighttime crowds into the area. Mass transit is available, and hotels and restaurants are proliferating -- all of which contribute to what Schwarz calls "the ceremony of going out.

"We really need to concentrate on an area of town that is not a parochial neighborhood -- one that embraces everyone -- and that is downtown," Schwarz said. "D.C. is in its midadolescence as a city. What it needs now is a strong downtown performing arts component. But if we continue to disperse our efforts throughout the city, we won't get a city."

About 1,500 copies of the study will be distributed to local developers, city officials and arts leaders. "It's our hope that the report will move the whole issue of arts facilities to the front burner of the city agenda," Shalwitz said. "It's intended as a catalyst. It says here's what you need to know to make an informed decision about theater space in Washington. It should lead to a discussion among a lot of the right people."

Titled "Downtown Stages: New Theatres for Washington, D.C.," the study was financed by $23,000 in contributions from the Eugene and Agnes E. Meyer Foundation, Robert M. and Ann T. Bass, and the D.C. Office of Business and Economic Development. Helping Shalwitz and Schwarz write it were Mary Ann de Barbieri, managing director of the Shakespeare Theatre at the Folger; architect Tom Greene; and John Fondersmith of the D.C. Office of Planning.