Elgar, Sir Edward: ''Enigma Variations,'' ''Pomp and Circumstance'' Marches 1 & 2, ''The Crown of India'': March. BBC Symphony Orchestra, Leonard Bernstein, conductor. (DG Digital 2532 067) This is not a record that will go over big with anyone who has certain ideas of how the ''Enigma Variations'' should go. Bernstein breaks all the ''rules'' set down by Elgar himself on record and followed by generations of important British conductors. Bernstein clearly adores this music. In fact, he dotes on it, sometimes to excess. But that love, that admiration for Elgar the orchestrator, that affection for Elgar the melodist, comes pouring out of the speakers from beginning to end. The two ''Pomp and Circumstance'' marches are performed with uncommon vigor. The ''Crown of India'' marches capture all the majesty of the British pageantry in a setting that speaks of heat and elephants. The recording is superb and a must for Bernstein fans. Even open-minded Elgarians will appreciate the utter beauty of it all and forgive the excesses.