Somewhere in America today, the pitter-patter of tiny reindeer hooves on the roof will be drowned out by the roar of a hot-air dirigible making a final approach on an unsuspecting chimney.

The 120-foot-long airship will glide in over the swimming pool (anybody who gets his or her own dirigible for Christmas must already have a swimming pool) and probably will set down somewhere near the Mercedes-Benz (Or is it a Rolls).

Yes, affluence fans, somebody's going to find that $50,000 "his and hers" blimps from the Nieman-Marcus catalogue hovering over the Christmas tree.

No, the buyer is neither a Texan nor a Middle East oil shiek, but "no more hints," insists Neiman-Marcus publicity man Keith Nix.

The dirigible is going to be a surprise.

Neiman-Marcus has sold three of the striped nylon airships since the catalogue came out, but only one will be delivered in time for Christmas. Even the rich sometimes have to wait their turn.

For the fortunate, first-in-line at the dirigible counter, the Neiman-Marcus airship will be delivered with what store officials call "appropriate arrangements,"

"I can tell you it will land," he says, totally discrete about other details.

The dirigible recipient will get balloon-piloting lessons along with the keys to the cockpit, a two-passenger gondola that hangs beneath the cigar-shaped bag.

Neiman-Marcus throws in a "a well-stocked picnic hamper" along with the $50,000 purchase and offers the dirigible in any color the buyer wants.

Made by Stokes Airships and Balloons, Inc., a Southern California firm, the Neiman-Marcus dirigible has a 72-horsepower engine that enables it to cruise at a leisurely 25 miles an hour.

Small compared with the Goodyear blimp -- 125 feet long compared with Goodyear's 192 -- the Christmas dirigible is kept aloft by hot air (supplied by a gas propane burner) rather than the helium gas used by the tire maker.

Nor is the dirigible the most expensive item in the Neiman-Marucs catalogue. That distinction goes to a gold, turquoise diamond and amethyst necklace with matching bracelet and earrings that carries a $125,000 price tag.

The necklace also will be under someone's Christmas tree, and the Neiman-marcus spokesman, who added, "We've seen no indication of any problem with inflation or people changing their expectations this Christmas." CAPTION: Picture, The Neiman-Marcus hot-air dirigible: a $50,000 surprise will be delivered with "appropriate arrangements." Neiman-Marcus