HOW SOON WILL the Filene Center at Wolf Trap come alive again? No one yet knows, and no one is more concerned than Catherine Filene Shouse, whose gifts made this public haven possible --and who now must turn to individuals, corporations and the government for help in rebuilding the center savaged by fire last month. So far, the response from individual donors has been heart- warming, says Mrs. Shouse. But the challenge remains staggering:

* If preliminary estimates hold, the grand total of public and private funds necessary to do the job could top $17 million. Officials do hope that the center's concrete foundation can be salvaged for a possible saving of more than $2 million. With about a half-million dollars in private contributions from the initial wave of responses, there is obviously a long way to go.

* Firm agreement is necessary soon on the schedule of help the government plans for replacing a facility that was uninsured because the government acts as its own insurer. Interior Undersecretary Donald P. Hodel has said that his agency will seek a 50-50 cost-sharing arrangement and that action should be delayed. But speed and definite numbers are important. If, for example, the National Park Service can redirect some funds right away, private contributors will have a clearer idea of how to respond.

* In Congress and around the country, those who have enjoyed the variety of free and low-budget events at Wolf Trap, as well as its major productions, need to emphasize that the campaign is not some narrow, highbrow appeal to wealthy arts patrons for a facility enjoyed only by the upper crust of the nation's capital. Visitors from every state, and local families that have shared the sights and sounds of Wolf Trap, can attest that this is a facility that belongs to and is open to everybody.

At this point, the people and businesses of Virginia are leading the way in contributions. They could stand some competition. Checks to the Wolf Trap Foundation, c/o The Postmaster General, Washington, D.C. 20260, can make a difference.