Washington fantasies.

The most obvious ones are about money and power, with sex a poor third. Everybody knows that.

But what about the other one? The dream that surfaces late at night with your most intimate friends -- when the lights are low, when you've pushed back your plate and are deep into the second bottle of wine.

It's the one that comes closest to your secret sense of self. The one that measures the miles traveled since the days when you didn't know a quiche from a Sara Lee cheesecake. The one that has to do with how tasteful you are:

"You know, what I'd really like to do is open a little restaurant. . . ."

The dinner-party refrain may be sung a thousand times a week by those who bake a pretty good bagel, whose dinner parties are famous, who labor over two porous stones to grind sesame seeds for the mole sauce, who make a terrific gumbo -- all those diners-out to whom running a restaurant appears the soul of simplicity compared with their own high-pressure jobs.

And who don't know what they're talking about.

"In Washington, the three most dangerous occupations are adultery, diplomacy and opening a restaurant. They do all three frequently, but probably opening restaurants is the most perilous," says George Lang, an internationally renowned restaurant consultant.

"We live in an age of what may eventually be tagged 'restaurantitis,' and it's an illness for which there's no cure," Lang said. "Not everybody thinks that he can build a house or carve a wonderful statue, but everyone seems to think he can open and run a successful restaurant."

"Everybody has a restaurant in them," said Mark Sandground, a D.C. attorney and "restaurant doctor" whose own ventures have included La Nicoise and The Washington Palm. "But it's a tough business."

It's a high-risk business with a high mortality rate. Nationally, there were 614 failures in 1980, compared with 449 in 1979, according to Dun & Bradstreet. But those figures don't include the number of restaurants that changed hands, which is the common outcome when things go sour.

Washington is generally a good town for restaurants. Its recession-proof nature, its expense accounts, its nonunion nature and an upwardly mobile population -- always looking beyond the next copper saucepan -- make the Washington area a slightly more stable environment in which to raise a restaurant. Even so, Washington has its share of failures.

The odds that a new, full-scale tablecloth restaurant will fail in the first year of operations are 40 percent, according to Washington restaurant broker Al Stern, who has watched countless restaurants change hands in 27 years. The used-restaurant business is somewhat less chancy, he said.

Running a restaurant "is generally pretty risky," agreed John S. Cockrell of the Restaurant Association of Metropolitan Washington, "A lot of people really don't understand that it's a business. They think it's an experience, I guess."

Fast-food franchises, which account for a rising percentage of the dining-out dollar, are almost a different business from tablecloth restaurants, with many of the risks removed and a generally higher rate of return.

It takes more money than many people opening restaurants realize, just to begin. Estimates for opening a first-class, tablecloth restaurant in the Washington area range from $3,000 to $3,750 a seat. That means roughly $300,000 to $400,000 for starters on a 100-seat restaurant. Generally, any financing arrangement will require a down payment of approximately one-third.

In addition to the money needed to acquire the lease and install or redesign the restaurant, the money for printing menus, the cost of equipment and food and the cost of hiring someone to haul away the trash, a beginning restaurateur also needs capital to sustain him or her in those critical first few months when things may not happen as planned.

"You spend most of your assets opening, because theoretically you will have money at the end of the day to pay bills," said Jim Niten, a sales representative for L. N. Hill Co., one of about half a dozen restaurant supply houses in the Washington area.

"At the end of the day, when someone comes in with a C.O.D. order that will cost you $100, you may have done hundreds of dollars worth of business that day but find you have only $6 cash in the register, because all the rest is paper," said Niten, who had a brief, undercapitalized whirl at the restaurant business himself.

A 1978-1979 study found that average net income before tax for restaurants was approximately 4 percent of total sales. On the average, an investor can make more money elsewhere -- but in a successful restaurant average net income can be as high as 15 to 20 percent of sales, according to Sandground.

Restaurant financing comes in all shapes and forms. In the Washington area, bank loans are a common type of financing, according to Sandground and others. Even so, finding a bank loan may not be easy because of banks' traditional unwillingness to lend to such high-risk businesses.

Generally the loans require a sizeable capital contribution to the business by the person seeking the loan and heavy security or guarantees. The length of such loans ranges from about six to eight years, with interest rates that are typically several points above prime.

The Small Business Administration is another major lender. Such businesses as The American Cafe have started out with SBA-guaranteed loans, although successful restaurants quickly grow beyond SBA's limits.

Still another style of financing is syndications -- "doctor-lawyer deals." A syndication may be aimed at either covering the entire cost of opening and operating a restaurant or at raising enough capital to convince a bank to lend the rest.

Although many professionals in the business warn against such deals, they seem to exert a strong attraction. In many cases, investing in a restaurant syndicate pays off only when the investor sells -- and a 5 percent share of a restaurant can be hard to unload. "You don't go into these deals for return on investment," said one professional. "You do it for the romance and the sex of the deal."

The perils in partnership include squabbles over control and too heavy demands on the restaurant by those who consider it theirs. In the case of one fashionable Southwest D.C. restaurant, according to Quinn and partner Stephen G. Strack, partners who had almost a year in which to ante up their contributions came in and ran up heavy bills entertaining their friends and clients in the meantime.

Restaurant equipment companies also finance restaurants and guarantee bank loans in return for security that includes all the equipment, the lease-hold interest and the license. When the loan goes bad, they foreclose and resell.

Other things that can go wrong include:

Overreaching. Nizam Ozgur, who runs a successful restaurant in Fairfax County, told of a friend who opened a restaurant in a southern city with sterling silver and $150 chairs. "Maybe very good chairs, but not good management," he said.

Waste. "It's a real killer in this industry," Lang said. "If you don't forecast how many people will be there and cook too much, immediately your very fragile profit margin is going to disappear."

Location. The best restaurants will be a success no matter where they are located, said several restaurateurs. Most of them mention Auberge Chez Francois in deepest Fairfax County as an example. For other restaurants, however, a block or two too far from the mainstream can spell the difference between success and failure.

Loss of control. It's a problem in partnerships and in growing enterprises.

"Now that we've grown to a certain size, we've reached a point where we're aware of a certain danger if there is not proper coordination between the restaurants and the cuisine," said Christian Doumergue, owner of the successful Bread Oven, La Miche, a Rockville bakery and a new branch of the Bread Oven in Spring Valley.

Service. "The last link in the chain is the waiter and the waiter's contact with the guest, how he presents you," Lang said.

Fatigue. Running a successful restaurant requires constant hands-on involvement that may wipe out virtually everything else in an owner's life.

What it takes to be a success includes money, training and preparation, location, a vision, commitment and a budget that covers contingencies.

"Everybody fails in this business," Lang said. "The trick is to keep the successes big-scale and the failures small things."