American Classic. Over the last half-century it has become one of the most respected of all schools of American organ-building. And perhaps no instrument today embodies that aesthetic more imposingly than the Mormon Tabernacle organ.

That was the aim of the present organ's original designers, G. Donald Harrison of Aeolian-Skinner and then-Tabernacle organist Alexander Schreiner. Just after he signed the contract that would produce the instrument that was finally unveiled in January 1949, Harrison confided in a letter: "With the location of the organ and the superb acoustics there is a real chance to build the most distinguished instrument in the country, and that is what I intend to try to do."This week, almost exactly 40 years later, comes another unveiling, of the most extensive renovation to date of Harrison's masterpiece. Undertaken by Jack M. Bethards of Schoenstein & Co. of San Francisco (which assisted Aeolian-Skinner in the 1948 installation), it represents in Bethards' words "not another step in the organ's evolution but rather a conclusion of Harrison's 1948 project."

The result is an instrument that, according to its current custodians, represents the state of the art in American organ technology without compromising Harrison and Schreiner's original vision. It also has become the occasion for an organ "event," the American Classic Organ Symposium, taking place next weekend on Temple Square.

Jointly sponsored by the Salt Lake City and Utah Valley Chapters of the American Guild of Organists, Brigham Young University and The Church of Jesus Christ of Latter-day Saints, the symposium is under the direction of Tabernacle organists Robert Cundick, John Longhurst and Clay Christiansen. Included will be lectures by Bethards, organ historian Barbara Owen and organists Thomas Murray and Robert Glasgow. In addition Murray and Glasgow (both of whom were consulted on the renovation) will perform in recital Friday and Saturday, beginning in the Tabernacle at 7:30 p.m.

You won't catch Cundick and his colleagues referring to the Tabernacle organ as a toy - they are too dignified for that. Nevertheless some of that enthusiasm spills out as they discuss the renovation and the potential it now gives the instrument, the latest in a long line of Tabernacle organs going back to 1867.

To those intimately acquainted with the instrument, the most visible changes are in the console, now located atop a disc that allows manual rotation of up to 180 degrees for optimal viewing during broadcasts and recitals.

"That was John's idea," Cundick says, "and Clay and I thought it was fantastic." But Cundick is even more excited about the microchip technology that permits faster and more varied responses, as well as enhancing the console's memory.

"When the organ was first installed in 1948," he explains, "it had 20 combinations that affected the entire organ plus settable combinations for each division, about six to eight in number. That was a lot for a large organ of that time, more than most its size had. But with microcircuitry and computer chips we have multiplied that so that every piston can be set on any one of 64 different memories. In addition the relay system was also partially a mechanical linkage. Solid-state wiring now makes it possible to speed that up in terms of microseconds, so the sound gets to you even faster."

Except for the digital readouts above the fifth manual you won't see any of that on the console itself, however, thanks to a "works-in-a-drawer" installation that has consigned those controls to the same kind of compartment on the organist's left that holds such odds and ends as pencils and paper clips on the right. Also included on the display bank are a clock, a stopwatch for broadcast timing and even an LED meter to monitor the crescendo pedal - as Christiansen says, "before it brings down the roof." And although the Tabernacle itself is not air-conditioned, the organist now is, thanks to a fan with tubular air ducts on either side of the console designed to take some of the heat off the performer during broadcasts.

In addition, Longhurst points out, "we now have the capability of reversing the lower two manuals (or keyboards) so we can have either a German-English configuration or a French configuration of manuals. Also some of the general pistons that occurred only on the left now are duplicated on the right-hand side as well, so if you're playing high on the keyboard they're right under your fingers."

Additions to the organ itself are equally subtle but, as all three organists point out, still in keeping with Harrison's original ideas.

"With Bethards we went back and researched all the correspondence on the organ in terms of `wish lists,' " Cundick says. Bethards was also able to talk with people still living who had been involved in the original installation. "What we found was that there were things talked about at the time that for various reasons were never actualized that we in fact did. For example, the addition of reeds to the great division - Harrison was never able to do that, but we discovered the space was there."

In all, according to Longhurst, the additions total 15 ranks, including two sets of high-pressure reeds, "to sing out above the choir or the organ when they're going full blast"; an 8-foot principal in the positiv division, "finally making it an adequate foil to the great"; a mounted cornet in the great division; and, a la the great 19th-century French organs, a flute harmonique. "It's just a fantastic stop," Cundick says of the last. "I don't know how we ever got along without it."

The project itself has taken four years, each component being added as it arrived. ("I think it took a full day to voice the montre," Cundick recalls.) Which means most of the "new" Tabernacle organ has already been heard by regular visitors to Temple Square or by listeners to Tabernacle Choir broadcasts.

Sometimes that called for fast work and tricky scheduling. "For example, we switched consoles twice without ever missing a noon recital," Longhurst points out. (The remodeled one has been in place since February 1987.) Nonetheless Cundick is grateful to the the First Presidency of the church "for seeing the importance of maintaining this organ as one of the great organs of the world and letting us do what was needed in the right way, in terms of time and money."

Along the way, Longhurst says, that meant the regulation of every pipe, old and new, in the organ "to see that it was putting out the appropriate sound in the appropriate quantity, and any anomolies were corrected." The result, in Cundick's words, "was fantastic, like polishing old silver."

And what difference is the average listener likely to notice? Among other things a new pungency in the reeds, which now speak more directly, and I think an increased presence overall, something all three organists promise will be exploited.

Lest you be worried that things have changed too radically, let me assure you it still sounds like the Tabernacle organ, to these ears instantly recognizable however one encounters it - i.e., in the flesh or over the airwaves. Bethards, who has compared its "signature sound" with that of the Philadelphia Orchestra, says up front that was one of his guiding principles - i.e., "that nothing could be changed or introduced which would rob the organ of its characteristic elegance in accompaniment and its eminent suitability for radio pickup."

Cundick sees that as a reaffirmation of the American Classic concept, namely "a multipurpose organ designed to play all types of literature. In some ways it's the equivalent of the modern symphony orchestra. Some people point out that isn't what Handel's orchestra sounded like, or Mozart's, and don't like the idea of one orchestra playing the entire breadth of the literature. But most people will take a modern orchestra over anything in the past. It represents hundreds of years of symphonic evolution."

By the same token the current edition of the Tabernacle organ is better suited to Bach than its forerunners were and yet is able to encompass both the romantic and modern literature as well - in some cases incomparably.

That's what Schreiner and Harrison were after, as were the renovators. And this week you too can hear the results, as all events are open to the public free of charge (including a pretaped video tour of the organ's innards).

For information call 240-3221.