The martini, said H.L. Mencken, who knew whereof he spoke, was "the only American invention as perfect as a sonnet."

President Franklin Roosevelt served a martini to Stalin at the Teheran Conference in 1943.

A generation of James Bond fans can quickly relate how the British spy preferred his martini -- "shaken, not stirred."

And historian Bernard DeVoto referred to a martini as the "supreme American gift to world culture."

Although Americans' taste for martinis -- one part gin, one part vermouth -- may have waned, the consumption of alcohol has not.

Toasts accompany almost every major social function from weddings and birthdays to dinners entertaining heads of state. During last week's summit, President Reagan toasted Mikhail Gorbachev with a California sparkling wine at the state dinner.

Alcohol "breaks down social barriers or awkwardness," said Dr. Mohan Advani, medical director of New Beginnings, an alcohol treatment program at the Psychiatric Institute of Washington. "It is a social lubricant between strangers or people who might be timid or shy."

And in the United States, the most alcohol is consumed during November and December, reports the Distilled Spirits Council of the United States. This fact places special responsibilities on hosts of parties -- sometimes even legal responsibilities.

It is no longer a matter of placing the drunk on his horse at the end of the party and letting the horse carry him home. The whole concept of drinking has changed because of the danger that comes with the machine age, said Bernard Mergen, professor of American civilization at George Washington University.

An estimated 23,987 Americans were killed last year in traffic accidents in which alcohol was a factor.

In 17 states, courts have held that a social host can be held liable if a person leaves their party drunk, gets in a car and has an accident, said James M. Goldberg, an attorney in the District. The District, Maryland and Virginia are not among these states.

For restaurant and bar owners, courts tend to demand an even greater level of responsibility. Recently, the D.C. Court of Appeals ruled that Washington restaurant owners who serve alcoholic beverages to a drunk customer can be sued if the customer has an accident after leaving the premises.

In Maryland and Virginia, the common-law rule -- that restaurant and bar owners cannot be held responsible for the actions of others -- still applies.

"I certainly would not advise anybody that just because the law says there is no liability that it is open season at Christmas parties," Goldberg said. Hosts and hostesses are encouraged to carefully plan a party to avoid alcohol-related problems.

The Washington Regional Alcohol Program (WRAP), a business and civic association concerned with drunk driving issues, recommends: Don't make alcohol the party's focus. Serve nonalcoholic drinks or "mocktails," drinks that look and almost taste like their alcoholic counterparts. Avoid serving salty foods, such as potato chips and pretzels, that make people want to drink more. Offer foods such as cheeses and seafood that help to absorb alcohol. Use a professional bartender; don't let people pour their own drinks. Close the bar at least an hour before the party ends. Serve dessert and have coffee and tea available throughout the evening. Coffee and tea will not sober up an intoxicated person, but they are a nonalcoholic alternative.

Despite the most careful plans, it is still possible that someone will be drunk at the end of the party. One way to prepare for such a problem is to contact a cab company in advance and let them know you are having a party and that there might be a need for a ride, said Doug Neilson, a representative and member of the board of directors of WRAP. "Pay for the rides in advance, and send the person home in the cab."

Designate a driver at the beginning of the party. To encourage the use of designated drivers at company holiday parties, the firm might consider rewarding the driver with a small gift or a day off, Neilson said.

Sober Ride, a taxi service that will take people home from a party if they are unable to drive, will be available from Dec. 11 to Jan. 2, 7 p.m. to 3 a.m., 578-HOME. The rides, paid for by Coors Beer and sponsored by WRAP, will only take a person home, not to another party, Neilson said.

Sometimes the best solution is to let the intoxicated person sleep on the couch.

If precautions are taken, drinking alcohol in moderation during the holiday season need not be a hazard.