With a recent Philips release, there are now 20 complete sets of Beethoven's nine symphonies. Some are indispensable historical documents, like Toscanini and Walter. Some give fine interpretations in fine stereo, like Bernstein and Karajan. And some don't give us much at all.

It once seemed a great thing to have just one such set, an event that finally came in the 1930s under Felix Weingartner. But having 20 sets symptomizes a condition considerably less than great, which is that at least half the performances are available to the buyer only in expensive bulk, all or nothing.

This inconvenient trend is not limited to Bulk Beethoven. It's Bulk Brahms and Bulk Bach, Bulk Tchaikovsky (the recent Rostropovich set of the symphonies) and even Bulk Bruckner (now there's a heavy set). In these cases, the listener is often the loser - for one may want a single performance but not all the rest or one simply may be unable to afford a complete set.

In the case of the Beethoven sets, no more than five or six of the complete versions are of such overall stature as to be worth the investment, and almost all of those best are available singly as well. But many of the rest containing all nine, most available only in bulk, may contain striking performances much to be desired singly, but not worth the price of all the rest.

Three such bulk sets have recently arrived, each in exactly the above category. They are the Beethoven Symphonies, inidiosyncratic, sometimes extraordinarily sweeping interpretations made in the Nazi-period Netherlands under Willem Mengelberg (Philips 6767 003-8 records); the Beethoven piano concertos, plus the Choral Fantasy, in glowing, supple and subtle performances by Alfred Brendel, with the London Philharmonic Orchestra and Chorus under Bernard Haitink (Philips 6767 002-5 discs); and the Brahms Symphonies, with three additional orchestral works, in the bold but frustratingly irregular interpretations of Loren Maazel with the Cleveland Orchestra (London CSA 2405-4 discs).

Here are three performances, one from each set, that judged on their individual merits, would be notable acquisitions.

Beethoven's Fourth Piano Concerto: This is the most human, the most poetic, and, some would argue, the most profound of Beethoven's five piano concertos. Its material maintains the limits of the human scale and resembles the patterns of the human voice - the chorale opening by the piano; the dialogue between the troubled strings imitating straight speech patterns and the consoling piano lyricism that constitute the entire middle movement.

This is Brendel's kind of music and this recording may well be the finest available. The shape of the music is always in clear relief; harmony, rhythm, timbre and structure are conveyed with broad rhetoric, but it is so poised that nothing gets thrown off balance in the process. One reason for this is Brendel's low-key technical control; his runs are remarkably even, his pearly tone never gets percussive, the trills are delicate and tender. And the orchestra, obviously conscious of taking part in a memorable performance, rises to the occasion.

This performance is a rare matching of interpretive and technical skills. One cannot imagine Philips' not eventually releasing it as a single.

Beethoven's Third Symphony ("Eroica"): With its 37-year-old sound and its sometimes exasperating interpretive eccentricities, Mengelberg's "Eroica" would be no one's first choice. But of all these nine performances, this one best demonstrates the kind of heroic eloquence, brazen abandon and virtuosity that typified the Amsterdam Concertgebouw under Mengelberg for four decades. Such a combination of precision with opulence has all but disappeared these days, along with, it must be added, some of the arbitrary violations of the score with which Mengelberg distorts the "Pastorale," for instance. With Mengelberg, everything had to sound heroic, even if it wasn't. But the "Eroica" did not get its title for nothing, and Mengelberg makes the most of it. Just listen to the kinetic energy of the scherzo and the bracing rhythms of the finale. That's real heroics.

Brahms' Third Symphony: The Cleveland Orchestra is a superb Brahms ensemble, as concertgoers in this city have long known. Indeed, probably the best complete stereo version of these works is by the Cleveland; it is, however, the one on Columbia under the late George Szell - not this new one with Maazel. But the sound on this new set is little short of spectacular. Just listening to so fine an orchestra reproduced with this kind of splendor is exciting. And in the Third Symphony Maazel rises to the occasion interpretively. It is a dashing, refined, passionate performance; it doesn't begin to compensate, however, for his Brahms transgressions in some of the otherworks.