Ford's Theatre, which has often found itself on financial tenterhooks, raised $1.5 million last weekend and will significantly expand its upcoming programming, Frankie Hewitt, Ford's producer, said yesterday.

The size of the windfall, which includes $1 million in pledges toward an endowment fund, surprised even Hewitt, who allowed, "All in all, it wasn't a bad weekend."

The contributions, she said, will allow Ford's to present at least three musicals next season and for the first time in its history conduct musical workshops in New York in an attempt to develop new shows.

Sunday night's gala brought in an expected $500,000, which will be applied to general expenses. What wasn't expected, Hewitt admitted, were six pledges totaling $1 million, which will form the nucleus of what she hopes to be a $5 million endowment fund by 1988, the 20th anniversary of the historic theater's reopening.

"It all happened in 12 hours," said Hewitt, who had long been looking for a major contributor to launch the endowment drive, but admitted that by the middle of last week all her prospects seemed to have fallen through. On Saturday morning, however, Gerald A. Freed, president of the Washington-based Freed Foundation, agreed to contribute $500,000. Hewitt planned to announce what she said was the "largest single gift the theater has ever received" in the course of Sunday's gala.

First, though, she informed philanthropist and longtime Ford's supporter Armand Hammer, who replied that $1 million would be a more impressive figure and promptly pledged $100,000. By Saturday evening, Hammer had raised the remaining $400,000 from a group of personal friends. Responding to his appeal with matching pledges were: the Oscar and Emma Getz Foundation in Chicago; Metromedia Inc. Chairman John Kluge and his wife Patricia; Los Angeles developer Guilford Glazer and his wife Diane; and Swiss investor Kamal Zeinal-Zade, who, according to one Ford's staff member, "had probably never heard of this theater before."

"It's a miracle the way it all came together in time for Sunday's gala," said Hewitt. "But when Dr. Hammer decides he wants you to do something, I guess you don't say no." Hammer, recovering from surgery in Los Angeles, was advised by his doctor not to attend the gala. Instead, he brought his doctor with him to Washington. Hewitt said Hammer then sent his private plane to Charlottesville, Va., to pick up the Kluges for the festivities, making sure that a hairdresser was on board for Patricia Kluge.

The $1 million endowment, which Hewitt called "a terrific start," will have the immediate effect of relieving the pressure on Ford's box office. "We'll have some money to try new things, develop new works, invest in the future. We'll be able to gamble," she said.

She and Ford's recently appointed artistic director David Bell are still working out plans for next season. But among the strong possibilities are "Portraits," an original musical by Bell about four generations of a Nebraska farm family and their attachment to the land; and a new version of the musical "Is There Life After High School," which flopped on Broadway several seasons ago, but has been rewritten. Ford's has recently been talking with the Goodspeed Opera House in Connecticut, a seedbed for musicals, about possible coproductions.

Bell also said Ford's will "now be able to do a couple of workshop productions a year in New York, the first one definitely in January." In a workshop production, performers and writers develop new material over a six- to eight-week period, then try it out before their peers or invited audiences. While the expenses can easily run $100,000, workshops are considered an economical way of determining a show's possible appeal, compared with the $5 million it routinely costs to mount a full-fledged Broadway musical.