HOW EXCRUCIATING it must have been for Catherine Filene Shouse to watch in the night from the rolling grounds of her beloved Wolf Trap Farm Park as those huge, wind-whipped flames savaged the Filene Center--destroying at age 11 what had become one of the country's most popular cultural assets. Certainly for all the millions from the capital area and from around the world who have savored the pastoral magic of Wolf Trap on a summer's night, spring's tragedy was depressing enough. But please turn now, if you mourn the loss, to the obvious and immediate response: to rebuild.

Everyone can help--just as everyone, rich and poor, could and did enjoy Wolf Trap--and already, many have said they will; there have been heartwarming offers of everything, from supplies to volunteer construction work to donations of all sizes. Such contributions are a fitting and essential tribute to the generosity and the show-must-go-on spirit of Mrs. Shouse, donor of the 117 acres on which the center stood as well as of the money that built the structure.

Neither the foundation nor the federal government, which has operated the facility, can be expected alone to underwrite the revival of Wolf Trap. But with public support, this season's entertainment can proceed in at least some makeshift way at the park--while out of the charred ruins of Sunday night can rise a new Filene Center for the years beyond.

The campaign is in motion on an encouraging note: President Reagan called Mrs. Shouse to express his personal concern and to note that his administration would support a reconstruction effort. Nancy Reagan, too, has offered to help. Northern Virginia Rep. Frank Wolf, who was with the Interior Department 11 years ago when fire severely damaged the center even before it could open, reported similar pledges of cooperation from Interior and from Capitol Hill, where swift efforts should be made to come up with necessary federal funds for the recovery. And in the office of Rep. Sidney Yates, who heads the House subcommittee that would act, there is critical support for a federal effort in concert with private assistance.

Private enterprise--local and national, large and small--can pitch in; so can the many entertainers whose financial well-being surely has been strengthened by their engagements at Wolf Trap over the seasons. The foundation stands ready to address the challenge of rebuilding--and welcomes your encouragement--which may be expressed to Wolf Trap Farm Park, 1551 Trap Road, Vienna, Va., 22180, or as the switchboard may allow, to 938-3810. If ever there were a time or an opportunity to thank Mrs. Shouse for the great source of inspiration and entertainment that she and her family made possible, this is it.