THE HIGH POINT of the National Symphony Orchestra's "Scandinavia Today" concerts under Mstislav Rostropovich last fall was surely the "Sinfonia espansiva," the exultant Third Symphony of Carl Nielsen. A new recording of this Danish masterwork has just appeared, on a Unicorn-Kanchana import from England, which preserves a concert performance given in March 1981 by the Danish Radio Symphony Orchestra under another Russian conductor, Yuri Ahronovitch (KP 8006, actually pressed by Philips in Holland).

Ahronovitch, 45, has turned up here and there on various labels over the past decade or so. He succeeded Guenter Wand as conductor of the Guerzenich Orchestra in Cologne in 1975, and last year became conductor of the Stockholm Philharmonic. None of his earlier recordings suggested the sensitivity or power in evidence here: This is a glorious realization of the "Espansiva," possibly surpassing even the high-voltage performance recorded by Leonard Bernstein with another Copenhagen orchestra for the composer's centenary year (CBS MS 6769).

Listeners who felt Bernstein's tempo for the final movement was too broad (I must say I did not find it so) will prefer Ahronovitch's more flowing pace--and those who love this work will rejoice in having two such distinguished recordings of it.

The singers in the slow movement--soprano Elisabeth Rehling and baritone Michael Wilhelm Hansen--are ideal in terms of both individual timbre and balance with the orchestra. Throughout the work there is an almost heady feeling of vivacity and spontaneity, without however, a single bar that seems headlong or untidy.

Actual concert performances are frequently charged with a tension and excitement that are far less likely to creep into a studio session, and for that reason "live" performances such as this one are certainly worth preserving, especially when sonic considerations are fulfilled as handsomely as they are on this disc. Most listeners, though, probably would prefer to dispense with applause at the end of a recorded performance, and in this case we have nearly four full minutes of it. But there is something more, too: about midway through the applause there is a Tusch.

This invariably exciting European tradition is not widely known on our side of the Atlantic, but the Chicago Symphony Orchestra used to honor such conductors as Bruno Walter and Pierre Monteux with a Tusch. It is simply the orchestra's public tribute to a conductor for an exceptional concert--generally given at the end of the concert, as here, amid the audience's applause, but now and then given when the conductor came out to begin the second half. The concertmaster would signal the timpanist, whose drum roll would in turn signal the brass section to rise and play its brief but stirring fanfare. Sometimes the gesture was planned during the rehearsal period, sometimes as late as intermission of the actual concert; it always had a spontaneous ring to it. The Ahronovitch "Espansiva" is the first instance known to me of a recorded Tusch; there is no question of its having been richly deserved.

Another live performance of another Scandinavian symphony under yet another Russian conductor (who heads another Swedish orchestra) is offered on a Swedish import pressed by Teldec in Germany with the quite apparent aural advantage of Direct Metal Mastering. It is Wilhelm Stenhammar's Symphony No. 1 in F Major, performed last September by the Gothenburg Symphony Orchestra under its principal conductor, Neeme Jarvi (Bis LP-219).

Stenhammar (1871-1927) was one of the patriarchs of the modern Swedish symphonic tradition. His First Symphony, completed in 1903, is not to be compared with the Nielsen Third, or with his own masterly Second (recently recorded by Stig Westerberg and the Stockholm Philharmonic on Caprice CAP 1151), but it is certainly worth getting to know, and could not have had a stronger advocate.

Jarvi, who drew enthusiastic response from the public, the press and the orchestras themselves when he appeared with the New York Philharmonic and the Philadelphia Orchestra a few seasons ago (but got a much cooler reception when he conducted the NSO two years ago), shows the same sort of commitment here that Ahronovitch does in the Nielsen, and the sound itself is stunning.