Carly and James Serenade Islanders At Vacation Spot of Presidents and Stars

AN hour after his concert on Wednesday night, singer James Taylor headed back to earth again: just a lean, balding man standing by his old, junk-filled car using a sponge to wipe the dew from the back window. Time to go home to his small house on the Vineyard.

Earlier he and his former wife, Carly Simon, sang together on stage in West Tisbury before 10,000 awed, riveted, mostly hometown fans gathered in a dusty, open field. Just two megastars coming together to sing for the first time in 16 years.

''Awesome,'' bubbled a teenager as the concert ended. ''I think they left earth.''

Whitney Andresen, another island teen, said, ''I had to be here. When ever again will you be able to see James and Carly together?''

On stage Taylor and Simon, with their husky and honeyed voices intact after all these years of life's tumults, performed under a banner proclaiming, ''Livestock 95.''

The forces that brought Taylor and Simon together benefited agriculture and architecture, and most of all, community.

Despite their marital split years ago, the singers have continued to live separately on the island, both appreciative of the lesser-known community spirit that prevails here year round. More commonly, the press paints the Vineyard as exclusively a summer playground for the rich and famous.

But other currents run deeper.

The venerable Martha's Vineyard Agricultural Society last year disassembled a fine old post-and-beam New Hampshire barn, and brought it piece by piece to the island to replace a crumbling structure used each year in the 120-year-old Tisbury Fair.

Volunteers from the island did all the work in taking it down, transporting the wood to the island, and reconstructing it.

So, when Taylor and Simon performed two nights ago, the huge stage was less than 40 yards from the site of the new-old barn. The concert raised money to pay off the barn costs and fund the activities of the Agricultural Society and 22 community organizations such as the Felix Neck Wildlife Sanctuary in Edgartown. Organizers estimate more than $150,000 will be raised from the concert and food sales.

Taylor sang first, backed by a seven-man band and three singers. He shifted easily between his trademark gentle songs and the energy needed for ''Copper Line'' and ''Shower the People.'' Then as the crowd roared, he said, ''Let's get Carly out here.'' She bounded on stage, her 500-watt smile beaming as the two friends embraced. She sang ''Anticipation,'' and half the audience knew all the words.

She dedicated the next song, ''Nobody Does It Better,'' to Taylor, saying, ''I honestly feel this way about him.''

Tickets at the concert were $30 to spread a blanket in the open field, and $100 for one of the 2,800 seats toward the front. Tickets for the concert sold out in the first few hours.

To keep the mainland press away, and protect the community atmosphere, concert organizers banned television coverage and still cameras. Much of the help and security at the concert was provided by volunteers who were given a free ticket and a concert T-shirt.

''We had three times as many volunteers as we could use,'' says Glenn Hearn, a trustee for the Agricultural Society.

''It's so wonderful to see the barn here,'' says Andrew Woodruff, one of the key organizers for the barn project. ''With everybody helping, it took about three days to raise it, and we're ready for the next 100 years.''

Mr. Hearn says that because of the barn-raising, and new community interest in the society, membership has jumped from 350 to 800. Life membership is a modest $100.

David and Judy Reed, from Indianapolis, are staying at a bed-and-breakfast on the island. ''The owner gave us two tickets,'' says Mr. Reed, standing in the long line to buy T-shirts for $15. ''This crowd is really civilized, not your usual concert crowd.''

After the concert was over, Taylor said, ''It takes me about three hours to come down after a concert. I think this one, even without much rehearsing, came off pretty well.''

Understatement, Mr. Taylor.