The Dow's in the dumpster; Chase Manhattan is laying off 5,000 workers. Wall Streeters definitely need a break today.

This may be why many of them are grabbing lunch at a financial district McDonald's that features a gloved doorman, a pianist playing "Some Enchanted Evening" on a candelabrum-adorned baby grand and a menu that includes espresso and cappuccino along with burgers and shakes. It's cheaper than Windows on the World and, unless one of the hostesses seats them in full view of the overhead stock market ticker, customers can forget about oil prices except as they relate to french fries."A very interesting change of pace," appraises a banking consultant seated at a marble-topped counter, looking up from his Wall Street Journal. Diners sound enthusiastic about the atmosphere and service, though one single-minded financier wrote in the leather-bound guest book, "Need Tokyo quotes at night." The restaurant draws bemused tourists along with the business types and handles about 4,000 transactions on an average weekday, including those transmitted via - what else? - Fax Your Macs.

Frank Madalone, owner-operator of this and seven commonplace McDonald's restaurants in New York, is very proud. "We wanted to make it really classy," he says. "I wanted a Taj Mahal." He even made a pilgrimage uptown to study the aesthetics of Trump Tower before he opened the restaurant's latest improvement, a shiny upstairs boutique that sells T-shirts, golden-arch earrings and a 20-buck transistor radio shaped like a carton of fries.

The two-story restaurant on lower Broadway, just a block from the World Trade Center, probably is the McDonald's Taj Mahal. The decor, designed by Equipment Manufacturing Corp. of Chicago, is heavy on marble and oak, mirrors and potted palms, with scarcely a hint of plastic.

The hostesses who seat customers and ferry over napkins and tear-open ketchup packets (some things resist upgrading) are wearing purple silk suits by Ellen Tracy. Someone has instructed them in the sort of accessorizing - twinkly little earrings, cameos pinned at the collar, single strands of pearls - that would enable them to stroll right into one of the office towers across the street and analyze commodities.

Sprays of fresh flowers embellish the counter, which is staffed by order-takers in tuxedo shirts and (attention, Frank) the wrong sort of black tie, the kind that hangs, but still. The food is mostly the basic stuff and no more expensive than the already inflated prices at many Manhattan McD's. A Big Mac costs $2.79 here; up on East 23rd it goes for $2.17, but there's no one playing songs from "The Phantom of the Opera." Besides, the breakfast pastries here come from an East Side patisserie. And reservations are accepted.

McDonald's has other themed restaurants around the country, including a rock-and-roll McD's in downtown Chicago with an old jukebox and Beatles memorabilia on the wall and a St. Louis McD's on a paddleboat anchored on the Mississippi. Food-folks-and-fun headquarters in Oak Brook, Ill., says such entrepreneurial efforts by its franchisees are encouraged and increasing.

That's probably because fast food has become what marketers call a mature industry, meaning that growth is slowing. McDonald's worldwide sales of $17.3 billion in 1989 represented only a 4.2 percent increase over 1988. "They're trying all sorts of new operations to try to increase penetration," says industry analyst John C. Maxwell Jr. of Wheat First Securities in Richmond.

During tough economic times, "fast food usually does all right," Maxwell says. "People move down from the more expensive operations." But fast-food restaurants are "recession-resistant, not immune," he warns.

Accordingly, Madalone has all sorts of plans for his upscale McD's. He's opened a new upstairs dining area called the Orchid Room, where he can imagine people holding business meetings, "power breakfasts, that sort of thing." He's already booking birthday parties. And what he'd really like, on weekends when the Wall Street crowds thin, is to host what in-store posters call "dazzling engagement and wedding receptions."

A unique entrepreneurial vision, no? So far, no takers.