"A lot of people in Georgetown only give money for UNICEF," complained the 12-year-old dressed up last night as a Virginia license plate.

Sure enough, a stern-looking butler answered the door at the Averell Harriman home on N Street and, with the utmost decorum, dropped a dime into each of the bags of four youngsters.

The Virginia plate, a Maryland plate, a chapstick, and a 12-year-old dwarf were accompanied by a reporter in Georgetown, as were other youngsters elsewhere in the city and suburbs in an effort to see how the rich and the famous deal with Halloween.

Many, lie Mayor Marion Barry, Sen. Patrick Moynihan (D-N.Y.), Sen. S. I. Hayakawa (R-Calif.) and Henry Kissinger were not at home when the trick-or-treating began at nightfall.

At the Smith Bagley's townhouse in Georgetown, however, a servant produced chocolate bars exquisitely arranged on a silver tray. A few doors away at the home of columnist Joseph Alsop, another servant offered candy in an old straw hat.

Wasington Redskins President Edward Bennett Williams had but one small bag of Milky Ways to offer vistors who ventured out to his pastoral estate in Potomac, Md. "We don't get any trick-or-treaters out here," Williams' son said. "I guess they don't like us."

Virginia Senator John Warner was caught by surprise when trick-or-treaters met him as he walked wearily into his townhouse in Georgetown.

"Say, let's get them all some apples and things," he said to a servant.

"We don't have anthing," the servant told him.

Warner refused to accept that and after disappearing inside for a few minutes, reappeared with a bag of marshmallows that had known better days and some after-dinner mints.

"Anyone need to go to the bathroom?" he asked, always the host, as the group departed.

At the White House and at the home of Sen. Edward Kennedy all costumed types were kept at a distance.

After a brief walkie-talkie conversation with a colleague, the Secret Service man posted at the entrance to Kennedy's home on Chain Bridge Road in McLean refused entrance to three youngsters and two adults.

If Kennedy had disappointed the group, he had not drawn the wrath of one Darth Vader who stomped away from the East Gate of the White House muttering, "I'm not going to vote for that guy. They wouldn't let us in."

The guard at the gate conceded that there were no Halloween plans at the White House, and in a nonpartisan burst, said that in his five years guarding White House gates no president had ever passed out anything to anyone on Halloween.

At the Hickory Hill estate of Ethel Kennedy in McLean, a sign near the front steps warned, "Trespassers will be eaten."

The reception inside was a good deal warmer, as large trays of candy, nuts, and cider were there for the taking.

"Mrs. Kennedy does this every Halloween," explained housekeeper Ena Bernard, as a fireplace blazed in an adjacent room lined with pictures of John and Robert Kennedy. "She and the children left five minutes ago to go trick-of-treating themselves."

Carol Forman, a well-known nutrition advocate and currently assistant Secretary of Agriculture, left Tootsie Pops and other sweets for visitors at her Chevy Chase Home.

Ralph Nader provided huge amounts of sweets for youngsters.

"We have Almond Joys, we have Snickers bars, Cracker Jacks, O'Henrys, and suckers," said the housekeeper at his home in the Dupont Circle neighborhood.

The four seasoned veterans of the Georgetown Halloween experience explained their tactics as they weaved past a number of Draculas.

The area between Q and N streets, they say, provides the mother lode of booty. Above Q, the houses are further apart, and the work is harder. It is not unlike mining.

Occasional joggers shuffled through the leaves on the sidewalks. The quartet concluded that there were a lot more Fonzies this year than last, and that the loot wasn't what it used to be. But, after leaving a reporter, they followed the pattern which has proven best for them.

"The smaller houses give the most," the dwarf said. "We stay away from the big houses. You always end up with butlers."