For the second time in five years, a gnarled 105-year-old bonsai tree, part of Japan's $4-million bicentennial gift to the United States of 53 bonsai, has been stolen from the National Arboretum.

Worth between $12,000 and $15,000 and considered irreplaceable, it stands barely 22 inches high. To the untrained eye, it might appear more of a candidate for kindling then a rare example of the ancient Japanese art of cultivating dwarf trees.

But the tree is so distinctive -- its half-dead trunk is bleached to a silvery white -- that larcenous plant lovers apparently can't stand living without it.

So, despite elaborate but admittedly erratic security measures instituted after it was first stolen in 1976, the needle juniper vanished once again from the halls of the arboretum, located at 24th and R streets NE, sometime Thursday night or early Friday morning.

"The place was open for a meeting Thursday evening," acting director Frank Santamour said yesterday. "It could have been taken from the pavilion when the group was given a tour. But our curator [who gave the tour] thinks he could just give a quick scan" and know that all the plants were there when he locked up.

The needle juniper, which normally grows to a height of 30 to 40 feet, was first stolen five years ago by a suburban plant lover who thought it was worth only $20. It was recovered when the young man with a green but sticky thumb was convinced by his girlfriend that it was exceedingly valuable. He left it anonymously on the steps of the arboretum, but was later arrested anyway and eventually pleaded guilty to a misdemeanor charge.

The missing Juniper was first discovered in Japan about 30 years ago, clinging to some crag in a very exposed and windswept location. Already naturally stunted by nature, it was then transplanted, its age estimated at 70 years, and trained to mimic in miniature its larger relative.

It was one of 53 bonsai of all varieties gathered together as a bicentinnenial gift by the Nippon Bonsai Society from the collections of the Japanese emperor, three former prime ministers and other bonsai enthusiasts.