A Newport Christmas. Warmed by thousands of poinsettias, its extravagant mansions take on a homey festiveness

CH^ATEAU-SUR-MER is a handsome house, a Victorian fortress of a place, but it isn't the Newport mansion that usually dumbfounds the visitor. Except at Christmastime, that is, when it comes into its own. This Italianate stone villa looks newer than the 18th-century-style mini-palaces around it, but actually it's a bit older. It was built in the 1850s, before the really aggressive architectural competition began among the society hostesses here. So the interior is warmer in feeling than those of the other mansions; it is Grandmother's house -- on a vastly more generous scale, of course.

The small rooms -- by Newport standards -- the jolly golden-oak Eastlake furniture and woodwork, the stained glass windows, the fanciful stenciled ceilings, the playful trellis pattern that runs up the open stairwell, make this a place for children.

It's a wonderful Christmas house. You can picture the four little Wetmores, children of the original owner, William Shephard Wetmore (governor of Rhode Island), running up and down the laurel-roped divided stairway. I feel sure they would have appreciated the fireplaces banked with holiday plants and the carved wooden mantels invisible under fir and holly, grapes and cones.

And the ceiling-high Christmas tree is a Victorian sure-fire hit: hung with fans and angels, bouquets of dried flowers, Japanese lanterns, lavender ribbons, candles, and hearts stuffed with potpourri.

Ch^ateau-sur-Mer was one of the few Newport mansions that was lived in year-round. Most of these flamboyant ``summer cottages'' were shut for the winter. When Mrs. Stuyvesant Fish and her group came for the season, what with servants and friends and bags and baggage, it was like a small army on the move -- not a journey to be undertaken more than once a year.

Thus, the Christmas decorations in Rosecliff are a fantasy of what Christmas might have been, had owner Theresa Fair Oelrichs and her guests spent the holiday at Rosecliff.

Mrs. Oelrichs's father was one of the discoverers of the Comstock Lode, the richest silver mine ever found in Colorado, and she once gave a famous party in her cream-colored ballroom -- to which all the ladies wore white dresses.

So Rosecliff, based on Versailles's Grand Trianon, traditionally decks the halls in snowy white. White poinsettias and paper narcissus line the famous heart-shaped staircase. More white blooms collect between the arched French windows of the ballroom, which look out on one side to green lawn and great stone urns and on the other to a stormy gray winter sea. White scallop shells, white lights, tinsel, and balls of sterling silver shine on the 18-foot tree in the peach damask salon.

I like to think that Newport's extravagant mansions take on -- if such a thing is possible -- almost a homey atmosphere at Christmas. Come to Rosecliff in the summer, and you keep visualizing F. Scott Fitzgerald lounging by the fountain (the ``Great Gatsby'' was filmed here, and echoes linger). But a house, any house, with a Christmas tree seems a place for family and friends.

The Elms, built by coal magnate Edward Berwind, is a copy of the Ch^ateau d'Asni`eres, near Paris. Mr. Berwind could afford it; it was said that there wasn't a ship on any ocean that didn't use Berwind coal. Decorations in this house are intended to represent an Edwardian Christmas, in red and gold, I was told, though the color of the poinsettias this season is really pink. But they are everywhere -- in front of statues, on the gold piano in the white salon, in the imperial-sized Chinese cachepots , framing the grand marble stairs where you enter. The Berwinds died childless -- and fortunately the house was saved from destruction by the Newport Preservation Society, which now owns and maintains all the mansions.

Nearby Marble House, home of the formidable Alva Vanderbilt, had a child living in it -- the hapless Consuelo, who was once confined to her room upstairs, with its splendid but heavy English baronial furniture, so she couldn't escape before her wedding to the Duke of Marlborough.

Consuelo later defied her mother's social ambitions, divorced the Duke, and married a man she loved. But it's too bad it didn't happen here: Marble House's gold ballroom is just the place for an 18-year-old to waltz blissfully until dawn. Gold leaf covers the walls, and gold faces peer down at you from above; there are two mighty gilded chandeliers, with trumpeting cherubs and forests of candles, and a mantel of fleur-de-peche marble surmounted by two bronze statues.

In December the mantel is shrouded in a welter of holiday red and greenery. But the pi`ece de r'esistance of the tour is the 18-foot Christmas ``tree'' of red poinsettias, 500 pots' worth, looking like a gigantic red bell.

There's no marble on the outside of Marble House -- it's modeled after the Petit Trianon in Versailles; the two-story entrance hall of golden marble gives it its name. The dining room is marble, too -- a light oxblood color. The centerpiece of the long table is a three-foot-high silver epergne of sheep and human figures surrounded by holly and red carnations.

If you drive along Newport's Bellevue Avenue, you can see these reminders of Versailles on either side of the road. There's the airy grace of Rosecliff -- set back too far from the street for you to pick out the scallop shells and laurel adorning the gargoyles by the front door. And Ch^ateau-sur-Mer, hiding its seasonal decoration within.

But you can pick out a few wreaths -- classic green, with plain red bows -- on the magnificent banklike fronts of Marble House and the Elms. And, in honor of the holiday season, these noble faades look friendly, almost welcoming.

All four houses are lit from dusk to 11. They are open only on weekends in the winter, from 10 a.m. to 4 p.m.

Receptions are being at one of the four houses on successive Sundays this month. The reception next Sunday, the last one, is at Marble House. Cookies, eggnog, and music are included.