Beneath a wandering moon

''Come out to the dock - quickly!'' I call to Cousin Henry. ''The moon's rising full, and tonight is the night of the year it's closest to earth. The Chinese used to celebrate this particular moon by giving parties where everyone wrote poems and . . .''

''I don't want to write poems,'' Cousin Henry grumbles, ''least of all to the moon. That's been done before, not just in Chinese. And I've seen moons before. And it's too cold to swim now. I prefer to practice my violin.''

I walk down the dock alone. Across the wide, briny river the moon pops up red as the sun where the sun rose this morning. The sun itself has barely gone out of business. Sun and moon, at least, are constants in a life full of shifting planets and stars, plus some moribund meteorites.

Footsteps on the dock. ''All right, it's a fantastic moon. Apricot.'' Cousin Henry dives into the paler peach disks of moon on the waves, and pulls himself sputtering back up on the splintery dock.

As he dries off, Cousin Henry discusses the moons of the Mediterranean. I counter with a moon remembered rising behind the Acropolis even before the sun set - or was it over the Parthenon? He remembers a moon in Cannes. I tell him of the hot orange moon over Bali which, by the time I arrived in New Zealand and the Southern Hemisphere, had become a globe of ice. He recalls a moon . . .

No. Let us live in the present. Let us focus on this moon, here, over St. Mary's County, a paling moon now, with scratches on its faces, as if in order to crowd its way out of the sea and into the sky, it had to fight a path through blackberry brambles.

This moon has gleamed also over Vorkuta, Soweto, Kampuchea, Buchenwald, and will again in the next hours.

For these instants only, may we ignore or even forget what else the wandering moon illuminates.

Cousin Henry dives in again, paddles downriver like a Galapagos turtle. I splash along in his wake. It's cold. No question but that we are here, now, under a harvest moon.

Up on the shore, pears are hard but ripening on twisted trees. The garden is bursting with tomatoes and squashes behind the yard-wide spider web which stretches between the gypsy moth tree and the ten-foot- high Jerusalem artichokes. The last fireflies sparkle the junipers. Overhead: whirr of bats, squawk of herons, the silent owl.

While we are here in the river turned platinum, the moon also shines through the windows of the cottage.

A peaceable kingdom there, and a warmer one. We left eight kittens and cats sacked out across the living room floor, while the miniature mice we've named Crepes and Suzette slalom among them unscathed. The dog, sprawled on the porch, grumbles at the raccoon reconnoitering the terrain of scraggly lawn but doesn't challenge him further. The chorus of tree frogs, crickets, cicadas, will continue all night. The praying mantis seems content with mosquitoes.

When we drip back up the dock, shivering now, we find that the various children have washed the dishes without being told. That means we can get back to our books, back to our endless discussions, back to our writing and music. Perhaps we might also write concise, Oriental-style odes to the moon.

''You live a perpetual childhood of summer vacations!'' I've been told by friends. ''An ivied ivory tower.''

Yes, if measured by such idyllic days and nights, this would seem a perpetual exile from the world's troubles. At least it has been a temporary refuge and resource. A visiting Indonesian named Dede began his book here. Natalia, a newly-arrived Russian painter, suffering cultural shock and creative block, finally broke it here on the dock and hasn't stopped painting since. Mohammud, a Malay poet, completed his historical epic here at the desk. Halim from Egypt worked on his opera here. Cousin Henry's multi-hued multi-stringed quintet will assemble tomorrow in pursuit of the ''Trout.''

At this rate I expect roses to bloom through the snow like Alpine lilies at the glacier's edge: so much germinates, grows, sometimes even blooms and fruits here beneath a lopsided moon, or the sun or, best of all, under the rain when one has no excuse but to stay on the porch or by the fire, and work.

Vorkuta, Soweto, Kampuchea, Buchenwald, are far across darker waters. But still they lurk there. Lead-colored muzzles of rifles gleam in the moon, no longer romantic but rather a source of danger, or light . . .

And although, as Albert Camus said in his Nobel Prize speech, the artist needs solitude to create, he must bring himself out of his exile wherever, in the midst of the privileges of liberty, the voice of some unknown prisoner at the ends of the earth cries for help, and he must use his art to make that voice resound.

Life is not all composed of, or composing, sonnets and sonatas. Tomorrow we must return to worlds that have need of us, and not for our wavering art. For the indifferent moon shines upon many and different rivers, and it isn't only in this one that we swim