WE MEAN no harm to the numerous theatrical activities now going on when we say that the best show in town at the moment may well be that spectular hillside and valley of 70,000 azalea plants at the National Arboretum, out off Bladensburg Road. Those lush blossoms have reached their peak this weekend - right on time.

We pretend to no horticultural expertise, but we know that Washington offers few greater beauties than the luster of those azaleas, and official say this year's are the best in some time - the pinks and lavenders in particular. Further, azalea experts tell us that we would be unlikely to encounter anywhere else such a range of color and length of blooming season as provided by the Arboretum's 1,200 varieties.

And if there is so sorry a thing as a person unmoved by the sight of azaleas in full bloom, that sad soul might try the viburnums, the tree peonies, the Chinese dogwoods or the wild flowers, now also at their peak of bloom on the Arboretum's 415 acres. Additionally, the rhododendrons are doing quite nicely, and the evergreen magnolias and the day lilies will be along a little later. From now through November's fall camellias something always will be blooming on the Arboretum's fields and slopes. And in the winter there are still the ferns, the dwarf conifers, the hollies and the bonsai. Anytime, a visit is worth it - but we just thought it was worth reminding you that right now is probably the best time of all.*