SAINT-Sae ns' Symphony No. 3, the one with the big part for organ, is one of the several now-familiar works rescued from near-oblivion by being used as demonstration material in showpiece recordings.

The latest of these, however, impresses with the work's musical substance as well as the virtuosity--on the part of both performers and sound engineers--involved in presenting it. The stunning performance is by the Montreal Symphony Orchestra under Charles Dutoit, with Peter Hurford at the organ (London digital LDR-71090, cassette LDR5-71090).

The brilliance of the Montreal orchestra has been a well-kept secret as far as most of us are concerned. It was only two years ago that this fine ensemble's first recording appeared--Ravel's "Daphnis and Chloe'," also conducted by Dutoit, who has been music director in Montreal since 1977. That gave notice that the Canadian players constituted one of this continent's first-rank orchestras, shaped and guided by a conductor who may be a latter-day Monteux. Subsequent releases--among them more Ravel--happily confirmed this impression, and the Saint-Sae ns is the most impressive of all so far.

In terms of interpretation and execution, this performance is a dream. It has drama, passion, elegance, style, spontaneity, polish--an ideal balance of flair and tastefulness--and the sound is surpassingly realistic. In virtually every attractive recording of this work in the past, one's enthusiasm has had to be tempered by a reservation or two: "if only this," or "if only that." In this case there is not a single "if only." When the outstanding recordings of this decade are surveyed, this one will be high on the list.

A huge and astounding "if only" spoils what would otherwise have been an exceptionally attractive Mozart record from London's Dutch sister company, Philips, on which Sir Colin Davis conducts the great Dresden State Orchestra in the Symphonies No. 39 in E-flat and No. 29 in A (the same two Mozart symphonies Peter Maag conducted in his National Symphony debut concerts last month). The digital recording, a co-production with the East German state record company (Philips 6514.205, cassette 7337.205), is done in by the insane layout.

Philips, justly recognized as one of the world's outstanding purveyors of recorded music, has always been a little remiss in observing the basic premise of the long-playing record, which is to present the music without interruptions of the sort dictated by the short playing time of 78s. In its series of Haydn trios by the Beaux Arts Trio, for example, nearly every one of the 14 discs contains three works, including one sandwiched between the other two in such a way that it is interrupted between movements for turnover.

The playing times of these trios are such that in most cases four, instead of three, could have been accommodated on a disc; but even if we didn't get an additional work, we might have been spared the gratuitous inconvenience of having to turn the record over in the middle of a 15-minute work. This is the sort of thinking--or lack of thought--that disfigures the new Davis Mozart release.

The new disc is the first one on which I have ever seen Symphony No. 39 spill over to a second side. The first three movements are on Side 1, the fourth on Side 2 with all of Symphony No. 29. What earthly reason might Philips advance for this irksome silliness? Surely not the question of timing, for Side 2 is actually about 40 seconds longer than Side 1 would have been if it had contained all of Symphony No. 39.

It's too bad, for the performances are splendid--not only far better than Davis' earlier ones of these symphonies, but among the very best available. The orchestra responds superbly, and the sound is both robust and well-defined. We may never know what possessed Philips to come up with this off-putting format, but if the company could be induced to recall these absurdly designed discs and replace them with a sensible edition in which each work is complete on a side, that could be a winner.