One of the great social divides is between people who love a costume party and those who believe, to quote a woman who stands firmly on the anti side of the chasm, "If people have to dress up in funny clothes to have a good time, they should stay home."

Perhaps they are remembering the terrible fate of Gussie Finknottle in P.G. Wodehouse's Brinkley Manor: ". . . here he was, if one could credit one's senses, about to take part in a fancy dress ball, a form of entertainment notoriously a testing experience for the toughest. And he was attending that fancy dress ball -- not like every other well bred Englishman as Pierrot -- but as Mephistopheles -- this involving, as I need scarcely stress, not only scarlet tights but a pretty frightful false beard . . ." Gussie, whose intent is to impress Madeline Bassett, has taken the advice of Jeeves that "the costume of Pierrot, while pleasing to the eye, lacked the authority of Mephistopheles." The fate of Gussie, thrown adrift in the London streets without money or keys tucked into those glaring red tights is as devilish as the costume he wears and has probably put a great many of Wodehouse's readers off fancy dress.

But for those who have persevered in their fondness for masquerade, we are closing in on the day when funny faces and funny clothes pack the parties and roam the streets. And no, it is not too late to call up 50 of your closest friends and ask them to join you in a masquerade on this spookiest night of the year. Halloween, unlike the holidays that blare their coming weeks in advance, sneaks up on us, and many a potential Mephistopheles finds himself with nothing to do.

There is still time to race to the costumers. Ninja is big this year, according to both Ronna Costumers, 1139 18th St. NW, and Backstage, 2101 P St. NW, who say it's all part of the way people respond to what's being shown in the movies or on TV.

"Because of 'Dynasty,' the ladies are dressing up more," says the spokesman at Backstage. But poor Alexis has to compete with all those gorillas and vampires preferred by people who consider Halloween a night to scare. Naturally, in Washington, political masks are popular -- and though it's not the kind of popularity poll most politicos would commission, President Reagan masks are number one at Ronna Costumers, with Nixon coming in second.

At Dream Wizards in Rockville, a wide selection of political masks nestle in among the devils and vampires: Castro, Khomeini, Prince Charles and Princess Diana, Tip O'Neill, Jimmy Carter. And for all those who want to look like a bigwig, a three-foot-high Reagan head. The shop, at 84 Halpine Court, Congressional Plaza, is hard to find. Call 881-7791 for directions.

The Addams Family is back at Stein's Theatrical Supplies, 1180 N. Highland St. in Arlington (522-2660). "Elvira and Morticia are big again," says a store spokeswoman, "and we've also had to reorder the Ninja costume. Everybody wanted one."

If you think that your friends are the kind who wouldn't bother to outfit themselves, you could stock up on the requisite number of inexpensive black eye masks and some theatrical makeup, and put out a large pile of scarves, old jewelry, old clothes and pieces of cardboard that can be cut into daggers or fashioned into a witch's hat. Your guests can then disguise themselves as they arrive.

You could serve traditional Halloween fare -- teeny weeny candy bars, for instance -- but unless your friends are determined to relive the halcyon days of youth, they would probably prefer a more adult menu. This does not necessarily mean dull. Let your food wear costumes too. What looks like just another plain pumpkin can open up to reveal a steaming stew. (Don't try to cook the stew in the pumpkin, though many recipes suggest it; it is a tricky thing to get the timing right and often as not the pumpkin's sides collapse and you are left with a trick instead of a treat.) Bread can be baked in a variety of shapes. A sheaf of wheat is appropriate for this harvest season. Just break off bits of the dough, roll them between your hands into ropes and shape the ropes into a sheaf on a baking sheet. The silhouette will lose some of its clarity as the bread rises, but it will still be recognizable. A crescent shaped new moon is even easier, and if you brush the top with melted butter into which you have dissolved a little saffron, or with a wash of egg yolk and milk, it will be properly golden.

There was a time when critics were convinced that masked balls encouraged licentiousness. If that isn't reason enough to have one in staid old Washington, what is?