The New Playwrights' Theatre, which has been working since late spring to raise $86,000 by the middle of this month or close permanently, has surpassed its goal and is now assured of having an 11th season beginning Oct. 12.

By Wednesday night, when the theater's board of trustees met to sanction officially the upcoming five-play season, the fund-raising campaign had netted $87,410 in gifts and pledges. The money will reduce the theater's accumulated debt by approximately 40 percent and will also provide a small cushion for the future.

"The only reason there wasn't dancing in the streets," said an NPT spokesman, "is because the meeting was held indoors."

In addition, the trustees authorized NPT's managing director, Todd Bethel, to negotiate with Actors Equity to permit the use of one or two Equity (union) actors per show. Up to now, NPT has relied on non-Equity performers.

"I am very pleased that so many people came to our rescue," said NPT's artistic director Harry Bagdasian yesterday. "I feel more secure now than I have in 10 years." He added that the theater will concentrate now on increasing the number of subscribers, which totaled 1,200 last season. To date, 600 subscriptions have been sold, but that money has been held in escrow pending the results of the fund-raising drive.

The theater's first production in the fall will be "Blood Relations," a drama by Michael Wright about an estranged son who returns to his home in Baltimore to avenge the death of his mother. Bagdasian is also planning the first professional production of Jim Leonard's "And They Dance Real Slow in Jackson," which was part of the 1979 American College Theater Festival, and two one-acts by Mark Stein, "The Groves of Academe" and "The Plumber's Assistant."