The New Playwrights' Theatre, now in its 10th season of producing original scripts, will close on June 30 if it does not raise $86,000 by that date, according to Harry Bagdasian, the group's founder and artistic director.

Bagdasian will make that announcement at a press conference today in the red brick building at 1742 Church St. NW, which NPT purchased not quite a year ago at considerably below market value.

Monthly mortgage payments of approximately $2,400 have contributed to the financial problems of the theater, which is also carrying an accumulated deficit of $21,000. The $86,000 NPT is seeking to raise would retire that deficit, cover a $41,000 shortfall projected for this season, and establish a cash reserve of $24,000 for an 11th season, beginning in September.

"Why drag this theater, limp and undernourished, into the next season? We think it is a very responsible position we are taking--to say, 'Look, we see trouble ahead,' " Bagdasian said yesterday. "I love this theater more than ever. But without more money, we will have to close it."

Established 10 years ago in the basement of a town house on 20th Street NW, NPT has produced more than 50 original plays from authors all over the country--among them "Hagar's Children," "Splendid Rebels," "Phallacies" and a half dozen Tim Grundmann musicals. In the process, its subscribers have increased from eight to 1,212, its staff from unpaid volunteers to eight full-time employes, and its annual budget from $800 to $260,000. Revenues from the box office and classes make up 52 percent of that budget.

Although NPT has been the recipient of corporate and government grants, it has lagged behind in individual contributions. As part of its "Keep New Playwrights Alive" campaign, Bagdasian said the theater will hold a benefit on May 8 in the Pension Building, keyed to the theme, "An Evening on the Orient Express," and will actively solicit funds from the private sector. Bagdasian has also invited several local cultural figures to attend today's press conference, at which he plans to read letters and telegrams of support from playwrights whose work has been honed at the theater in the past.

"We have a recognition problem in that we are better known outside this city than in it," NPT's managing director, Todd Bethel, admitted yesterday. "That has caused us immense fund-raising problems in Washington. Corporate sponsors like Exxon want to see local support if they are to continue with their funding."

Today's announcement does not jeopardize the two remaining shows in NPT's season--an evening of three one-act plays, the winners of NPT's annual one-act play competition, opening April 14; and Ernst Joselovitz's full-length drama "Jesse's Land," opening June 14.