Wolf Trap announced yesterday that its entire summer season will go on, except for 14 New York City Opera performances, in a fabric and frame temporary structure on a meadow next to the Filene Center, destroyed by fire on April 4.

The Meadow Center, as the prefabricated modular building will be called, was used recently at a trade fair in the United Arab Emirates on the Persian Gulf. It had been dismantled and will be shipped here May 1--scheduled to arrive in time for a June 16 Wolf Trap opening. That is a week later than the gala opening planned before the fire.

All performances of that first week were to have been a new City Opera version of Franz Lehar's "The Merry Widow." "After the fire, there was no way we could get the space in a temporary building to fly their scenery," explained Wolf Trap's founder Catherine Filene Shouse yesterday at a press conference staged on the entrance plaza of the Filene Center as a chill breeze rattled the loose roof metal of the ruins behind her.

The new free-span building is a tan polyester panel structure supported by aluminum truss arches. "It is shaped a little like a Russian dome, not quite an onion shape," according to its manufacturer. It will be 260 feet long, 100 feet wide and 50 feet high, with substantial backstage and wing space; also it will have full lighting capabilities and "a state-of-the-art sound system."

Two thousand people will be accommodated on chairs in the orchestra area and a slope rising out of the meadow will allow a lawn audience of 4,500. The Filene Center had more seats inside, but the overall capacity at the Meadow Center is about the same as at the Filene Center. All seats will be general admission. "We simply could not have reserved seats under these circumstances," said Edward Corn, Wolf Trap's executive vice president and general director.

The module, built by Sprung Instant Structures Ltd. of Alberta, Canada, was chosen because of its speed of construction and the cleanness of its sight lines, said Ann McKee, Wolf Trap's director of production. Esthetics had to be secondary; "It will be somewhere between an A-frame and a Quonset hut in design," said McKee.

Putting up the Meadow Center will cost $800,000, Corn said; $370,000 of that will finance the structure and the rest will pay for site preparation. Costs will be split half way by the federal government and Wolf Trap, with a park service contribution out of existing funds.

"We have arranged to have it aboard ship in the Emirates by May 1," said Bruce Ervin of the Canadian firm, "and it is scheduled to arrive in this country May 27. We would have nine days to put it up after it reached Vienna, Va. That means working 24 hours a day. The only thing about doing it by sea is that they don't always arrive on time, but from the figure they are using it sounds like they are not going to fly it."

According to Daniel Rule, the New York City Opera's managing director, efforts to book the opera elsewhere here, including the Kennedy Center, have failed. "We are still trying to book the seven performances of 'The Merry Widow' in various cities.

"The principal financial loss . . . is employment for our singers," he said.

Providing a temporary facility imposes additional fund-raising burdens on Wolf Trap. Before the fire, Wolf Trap had to raise $2 million to break even. Carole Harford, president of the Wolf Trap Foundation, said at the press conference that "this shortfall is now up to $2.5 million."

That sum is separate from the $17.5 million cost estimated by the park service to replace the Filene Center. Shouse announced at the press conference a new matching grant of $100,000 from Mobil Oil, the first such large corporate contribution to come to the fund. "They approached us first and asked what they could do," she said later. "At first we gave them a larger figure and they said they couldn't do it. So we are glad to have what they have given."

Shouse declined to give the total sum of money raised so far, but said, "It is not as much as you would think. People seem to be still making plans and waiting to see what the government does."

Asked what form a rebuilt Filene Center should take, she said, "I think most people want the old form back. It's comfortable and most people like it."

Shouse said she accepted the park service's $17.5 million estimate, which she said was reached by taking "the $2.3-million original cost and adding in the inflation rate of each year."

Among the highlights of the Wolf Trap season will be a five-day jazz festival, a National Symphony series , a bluegrass festival, Abel Gance's film "Napoleon," "The Sound of Music," the San Francisco Ballet and Lena Horne's current hit show.

Three fund-raisers for Wolf Trap are presently scheduled: at Constitution Hall on June 9, with the Preservation Hall Jazz Band and the Marine Band; at the Kennedy Center on July 30 with Mstislav Rostropovich playing his cello, and pianist Rudolf Serkin; and another one planned in September at the Capital Centre under the chairmanship of Elizabeth Taylor.