The lavish gardens of Exbury, cleared and planted by Lionel de Rothschild 60 years ago, blaze forth in all their pink and orange tonight on "The Glory of the Garden," at 10:15 on Channel 26, with James Mason and Edmund de Rothschild narrating the hourlong documentary.

Exbury is not always reckoned among the most glorious of British gardens for all its size (250 acres), probably because it specializes so heavily in rhododendrons and azaleas. While these woody plants, deriving largely from wild plants of the Himalayas and the forests of the eastern United States, are spectacular enough, there is a subterranean feeling among refined critics, eh, that the gaud goes rather far in these bouncing and well-endowed beauties and that the best people do not go berserk over them.

As early as the close of the last century it was recognized and widely warned that the tender innocence of a northern woodland could be ruined by a too-free indulgence in botanical conflagrations. No sooner did the English all agree to this in principle than the English led the world in massing scarlet, magenta, rose and whatnot from one end of the realm to the other, wherever acid soil permitted their culture. Sometimes a shred of modesty was maintained in these woodlands by excluding azaleas (which some said were not good mixers with rhododendrons because of color clashes) or by excluding orange or yellow or some of the scarlet hybrids made possible by new species from Nepal and Tibet.

Either the Rothschilds missed the argument or found it asinine. In any case, at Exbury the woods are not only heavy with rhododendrons in all known and unknown colors, but also with azaleas, including some of the dazzling orange, lemon and tawny-hot ones actually bred there.

It is all very well to reflect on the austere beauty of birches and junipers and oaks with a few bluebells, but if you discover that rhododendrons grow like weeds with you, and especially if you start raising thousands of new ones from seed, it is expecting more than may rightly be expected of any gardener that he will settle for a touch of mauve and two citrons.

At Exbury they went hog wild, if that is not disrespectful to the home garden of so many of the world's most exquisite rhododendron hybrids.

As an English peer has pointed out (not Lord Rothschild and not in this program), few gardening pleasures surpass a visit to a great garden stuffed with marvelous things that one has strong reservations about. People who cannot grow the Chinese, Indian and Tibetan rhododendrons often point out there is something flamboyant and vulgar in having too many of them in the eye at once, but this is perhaps like a shop clerk's observing that a diamond should not be so large as the Kohinoor--a fiftieth of a carat is about right.

Several dogs appear in the film (some of the footage is old and wonderful and documents the building of the garden), all of them loping along with the air that only pampered and overloved mutts display.

Edmund de Rothschild says he speaks to the rhododendrons as he talks to (or with) the dogs. This may be why rhododendrons are all over the place. GOOD boy. WALKIE. Everywhere.