Imagine your friends' surprise when they come to a party at your house, ring the doorbell and are greeted by a perfect stranger -- a butler. Whether you've planned an elegant dinner for 10 or cocktails for 40, hiring a professional butler can make your holiday party as smashing as those of the glitterati. If your tastes and wallet dictate less opulence, you can easily find trained bartenders, experienced college students and others who will turn holiday entertaining from drudgery into fun. According to Jerry Croce of Lansdowne Caterers in Georgetown, one person can usually serve a seated dinner party for 10 people or a cocktail buffet for 20, if the host or hostess takes responsibility for food preparation. Two helpers are needed for groups of 30, and as you edge toward 40 or 50 for drinks and food, you should consider having at least three waiters or waitresses. Establish a clear party plan: how long will the guests linger over drinks, when should the meal be ready, and who cleans up? If your party is small enough to require only one helper, you will want to hire a jack- or jill-of-all-trades, a person willing and able to do a little bit of everything. In more traditional days such a person was called a butler, and he was always male. Today the proper appellation is waiter or waitress, and many more women are found in the ranks. Jim Nelson, who has served as a butler for almost 40 years, working at the White House and some of the grand homes in town, and who is a member of the Professional Butlers' Association, describes the range of a butler/waiter's duties: "He (or she) can take coats, greet or announce guests, tend bar, prepare hors d'oeuvres or food for service, serve, empty ash trays, refill glasses and clean up. He should be sensitive to the mood of the party and keep things running smoothly. Before the party he can help a host decide what quantities of liquor and mixers to buy and he can advise on placement of bars or tables. He should arrive about an hour early with the proper dress for working and serving." A butler can help decide whether a second helper is needed and how the work should be divided. Deciding what kind of help you need is easy. Finding the right people to fit your party and pocketbook is a little more difficult, but hardly impossible. You can find them through word-of- mouth, or through a professional organization. You can call a local union, university or bartenders' school for recommendations, or ask for help from caterers, or friends in the military who may know of waiters or bartenders who work at officers' clubs and who want to moonlight. Once you have found your party help, here are a few do's and don'ts to keep in mind: Call far in advance to make arrangements. One month ahead is best; two weeks ahead is still reasonable. Forget about getting popular waiters for major nights like Christmas and New Year's: they've probably been booked up for a year or more. Reconfirm about 10 days in advance if your help hasn't checked back with you. People forget. Make clear over the phone exactly what each person's responsibilities will be. That way, your people will not be falling over each other. If you hire a bartender, remember that many bartenders will not assume waiters' duties. Ask for references, especially if you have not gotten a recommendation from someone you know. And check the references. Do pay your help at the end of the party, and do tip, especially if someone has done an outstanding job. Tips needn't be high -- $5 to $10 is typical. Don't say "I'll put the check in the mail." Your helpers have proba average charge for experienced help is about $12 an hour, with higher rates for late night or holiday work. Most waiters ask for reasonable cancellation notice, even as late as a day or two before the party. Most expect payment if you cancel at the very last minute -- after all, they have turned down other jobs to take yours. Help gotten through any of the larger caterers can cost about $50 for the first four hours (four hour minimum), and $15 for each additional hour.

FINDING HELP

Here's a sampling of the party help available and what they charge.

PROFESSIONAL BUTLERS ASSOCIATION -- $50 for the first four hours, $10 for each additional hour. Double time for major holidays. No phone numbers available: word-of-mouth only.

ASSOCIATION OF PRIVATE WAITERS -- $40 for the first four hours, $12 for each additional hour. $12 per hour after 2 a.m. Double time for major holidays. Extra charge for jobs beyond 20-mile- radius of the city. Call president Ricardo Comas, 244-8492 or secretary, Manuel Rodriguez, 593-4884.

FOR PARTY SERVING & COOKING -- Call Vincent Queen, 853-2448, or Bob Allen, 829-5770. $50 for the first four hours, $20 for each additional hour. Willing to give party planning advice even if you're not using help, and will do catering.

HARVARD BARTENDERS SOUTH -- $10 an hour for the first three hours. $15 for each additional hour. Some serving. Call Cameron, 363-8036 or Andrew, 671-7826.

JAYE HANSEN CUSTOM BARTENDING SERVICE -- $20 an hour, three hour minimum (including a half-hour setup time). $5 extra an hour after 1 a.m. Bartenders supply all bar juices, fruits and implements. Some serving. Call 971-5297

UNION HELP -- $50 for the first four hours, four hour minimum. $10 for each additional hour. Outline your needs and they will have someone call you back. Call Local 25 and ask for Ron Richardson or Rene, 737-2225.

BARTENDERS' SCHOOLS

PROFESSIONAL BARTENDING SCHOOL OF THE HOTEL & RESTAURANT INSTITUTE -- $10 per hour. They will have waiters and bartenders call you. Make arrangements with them at least two weeks before your party. Call 821-8570.

INTERNATIONAL BARTENDING INSTITUTE OF ALEXANDRIA -- $10 per hour. Mostly bartenders, few waiters. Graduates will call you. Call 931- 0116.

BARTENDERS' ACADEMY -- $10 per hour. Mostly bartenders. Placement service sends out graduates. D.C., 789-0833; Laurel, 490-9400; Woodbridge, 494-8182.

COLLEGE STUDENTS Students set their own rates but generally it's $5 to $10 an hour, depending on what services are required and whether formal wear is expected.

AMERICAN UNIVERSITY -- Call the Career Center, 686-2067. They will take job listings and students will call you.

CATHOLIC UNIVERSITY -- Call Career Services, 635-5623. They will take listings and have students call.

GEORGETOWN UNIVERSITY -- The Career Planning and Placement Office, 625-4071, has files of bartenders and waiters. You must stop in and look through them: the office does not take or give listings over the phone.

GEORGE WASHINGTON UNIVERSITY -- The Career Services Office, 676-6495, will post a notice for you. They can also supply names of students who are experienced waiters and bartenders.

HOWARD UNIVERSITY -- Call the Student Employment Office, 636-7509. They will take listings and students will call you.