The music of George and Ira Gerswhin is having a second spring on Broadway in ''My One and Only.'' Actually it's closer to a sixty-second spring. Their brilliant matchings of melodies (George) and words (Ira) have never gone into hibernation since ''Lady, Be Good!'' and ''Someone to Watch Over Me'' lighted up the 1920s.
No wonder that, when George passed on many years ago, Ira felt a deep despondency - until he put on a Fred Astaire-Johnny Green recording of their music.
''In a few moments,'' he wrote, ''the room was filled with gaiety and rhythm, and I felt that George, smiling and approving, was there listening with me - and grief vanished.''
No wonder tha4, wyth Ira's passing last week, we feel a similar sorrow - and then try to honor him by recalling his example, letting the Gershwin gaiety and rhythm fill the room once again. And who needs a recording to remember ''Love walked right in and drove the shadows away . . .''?