THE REHAB OF the Seattle Center Opera House doesn’t even start till January 2002, but Seattle Opera and Pacific Northwest Ballet are already trying to figure out how to prepare their 30,000 subscribers for 18 months of exile. Based on an early look at designs for the facility meant to replace the Opera House while it’s being transformed into Marion Oliver McCaw Performance Hall, they’ve got a whole lot of preparing to do.

By and large the Center’s “principal tenants” for the Opera House have bitten the remodel bullet, not only agreeing in principle to help raise $60 million or so to cover the rehab’s current estimated $125 million cost, but committing as well to remain loyal Center tenants by performing during the season and a half of their displacement in a temporary auditorium built just for their use inside the cavernous 6,000-seat Mercer Arena just down the street from the Opera House.

Well, not quite a season and a half, because according to PNB’s new executive director David Brown, the Ballet is in active negotiation with Seattle Theater Group to book STG’s Paramount Theater for its month-long holiday run of Nutcracker in December 2002. But otherwise the Opera and Ballet appear to be committed to performing in the space jury-rigged within the Arena at an estimated cost of $7 million.

The Arena is not an ideal auditorium even for high-school graduations, basketball games, and rock shows. To make it even marginally suitable for the demanding arts of music-drama and dance, LMN Architects proposes reconfiguring the space radically, blocking off nearly half its volume with a corrugated 75-foot-high east-west wall, then providing seating for upwards of a thousand on a banked platform linking the hall’s flat floor with the concrete balconies that surround the space on three sides.

Sight lines for the majority of the audience in these seats will range from first-rate to not-bad, though the back seats of the balcony are more than 40 rows from the front, with a sizable “orchestra pit” intervening between seating and stage. Those relegated to the bleacher-style accommodations in the side balconies won’t be so fortunate, with at least several hundred seats set (in concrete) at angles guaranteed to produce cricks in the neck and sprains to the spine. When longtime Opera subscribers begin to realize how crucial seat assignments in the temporary hall are going to be for their physical well-being, expect the fur to fly.

The Opera plans to begin “educating” its subscribers about the Arena in the program for its upcoming staging of Lucia di Lammermoor. But sight lines may turn out to be the least of the Opera’s worries. General director Speight Jenkins is already telling subscribers that singers may well require amplification to be heard. There’s little point now in speculating about the more subtle acoustical properties of the concrete-walled, concrete-floored space, since no one will be able to predict them until the facility is 95 percent finished.

The sum of $7 million may seem pretty modest to cover the cost of constructing, maintaining, and dismantling a temporary 3,000-seat opera house. And indeed it is: According to project development manager Maria Barrientos, a veteran of the ACT and Paramount remodels, no money has been allocated for removal of the “temporary” structure, providing a rich opportunity down the line for argument about who has to pay.

As long as the structure’s in place, the Arena can’t be used by many of the customary tenants who lease it some 100-plus days a year now. But to keep its principal tenants in residence during the Opera House renovation, Center management has been willing to sacrifice the income and goodwill of these groups who’ve depended on the facility for community events.

FINANCIALLY, Seattle Center is unusually well-positioned to embark on such an ambitious project: Thanks to a massive up-front gift of $20 million from the McCaw Foundation and a cool $10 million from the Kreielsheimer Foundation, the Center and its own nonprofit private foundation have some time to work on raking in the remaining cash needed to finish the job. There are hopes for $17 million from county and state governments. Another $40 million or so is supposed to come from “the public”: code for benefactors who already support the Opera and Ballet, and who, it’s hoped, will respond as they have in the past to the “opportunity” to give even more lavishly for bricks and mortar than they already do to underwrite annual operating costs.

Assuming that the economy remains lively and interest rates relatively low, the Center’s number-crunchers are confident they’ve built enough slack into the budget to allow for the unforeseen, though more than half the design on the project remains to be done. At $125 million, they’d better hope so. The renovation is already tabbed to cost more than half again as much as the first estimates.

But one great unknown remains in the equation: the Opera House itself. Center director Virginia Anderson, who’s worked on such projects in the private sector in the past, says, “You never know when you start rehabilitating an old structure like this what you’re going to find.”