Facing rapidly mounting debts, the New Playwrights' Theatre will close permanently if its board of trustees does not raise $250,000 in the next 90 days, theater officials said yesterday.

The decision, disclosed by Arthur Bartow, New Playwrights' artistic director, and B. Thomas Mansbach, chairman of the board, comes one week after the Folger Shakespeare Library announced that it would dissolve the Folger Theatre at the end of the season and underscores a growing crisis in the Washington theatrical community.

Since its founding in 1972, New Playwrights' has been devoted to producing original scripts and has earned a reputation as one of the liveliest of Washington's small theaters. But in recent seasons, it has been plagued with debts, which now total approximately $300,000. After the current show, Elizabeth Swados' musical "The Beautiful Lady," ends its run on Jan. 27, the theater has no attraction until mid-April, when storyteller Spalding Gray is scheduled for a four-week engagement. The theater has 850 subscribers; its proposed budget for the season was $425,000.

Nearly three years ago, New Playwrights' found itself in similar straits and announced that it would fold unless $86,000 was raised. That drive was successful, but in November 1983 a fire set by an arsonist destroyed part of the facility and suspended performances for three months. Bartow conceded that the current crisis is of far larger magnitude, however, adding that "our greatest problem is that we've cried wolf so many times in the past."

With no money to produce any more shows in what had been announced as a six-play season, trustees considered temporarily closing the theater after Gray's engagement and then concentrating on fund-raising and financial reorganization. "In light of the news out of the Folger, the board decided instead that it had to move forward fast," said Bartow.

The theater plans to expand immediately its board of trustees from 19 to "about 35" and will hire a professional fund-raiser by the middle of next week, Mansbach said. Another trustee, Jackson Bryer, yesterday described the fund-raising plans as "not simply a matter of survival, but an effort to get better or close. We could scale down, but we have made the choice to scale up. We want Arthur Bartow to be able to do the kind of theater he wants to do."

Bartow was hired in July as artistic director to replace Harry Bagdasian, who started the theater in the basement of a Northwest town house. Said Bartow, "This theater has been operating on empty since the day I arrived. Any money that comes in goes out instantly." New Playwrights' is carrying mortgages totaling $230,000 on its present quarters, a 125-seat theater at 1742 Church St. NW, he said, and it has additional outstanding bills of approximately $70,000. A reduced staff of four employes has been paid irregularly in recent months.

"Washington is a tough city for any kind of small theater group to survive in," commented New York producer Joseph Papp, a member of New Playwrights' board of advisers. "Audiences alone simply cannot support them. They need outside money, and that should be evident in Washington, home of the National Endowment, from which money is distributed all over the country."

Including the Folger Theatre in his observations, Papp said, "The loss of two smaller theaters may not seem like much. But if these two go, a couple of more may go, and then what does Washington have? The smaller theaters are the bright spots; they provide the color. The irony is that they cannot be created with money -- they're wrought out of a lot of people's blood over the years -- but money can save them."

Bartow submitted his resignation last month, but he was persuaded to change his mind when trustees agreed to the massive fund-raising drive. "I had hoped to work exclusively as an artist in this institution," he said. "I think they the board saw me coming in waving a magic wand and thought that funding would drop in their laps."

New Playwrights reaches a considerably smaller audience than the Folger, but as the city's only theater devoted almost exclusively to original works, it occupies a unique niche and has helped lend credibility to the notion of Washington as a lively theatrical center, independent of New York. It has given a hearing to hundreds of playwrights here and across the nation; among its successes are "Hagar's Children," "The Diviners," "Splendid Rebels" and a series of original musicals by Tim Grundmann.

Annually since 1981, the theater has given the Richard L. Coe Award (named for the Washington Post's drama critic emeritus) to the person who has made a "significant contribution to the development of original material for the theater." Past honorees include Papp, literary agent Audrey Wood and Kennedy Center Chairman Roger Stevens. Presentation of this year's award has been postponed until the financial crisis is resolved.

The hiring of Bartow was seen as the next stage in New Playwrights' development from a grass-roots experimental theater to a small professional theater. Bartow had begun increasing the number of perfomers belonging to Actors Equity, the professional union, and had significantly improved production standards with his first two shows -- "Burial Customs" and "The Beautiful Lady." Yesterday's disclosure, however, raised the question of whether Washington is capable of supporting a broad range of theaters, as they now exist.

Although the city's small theaters live perpetually on the financial edge, soaring costs and dwindling subsidies have affected all theaters in varying measure. In October, the Kennedy Center announced that it had posted a $2 million loss for fiscal 1984 -- the first since it opened in 1971.