Another weekend, and as December slips by, you have a sudden attack of the holidays. Swamped with greeting cards, blasted by canned carols at subway stops, fed up with potato latkes and Santa cookies, you haven't really relished the business so far. Before the Scrooge in you takes hold, savor the season with a new slant.

Las Posadas is almost here. Mexico's nine-day fete starts Tuesday, so get a jump on the pinatas. A bit unfamiliar with the Posadas celebration? Nightly from December 16th through the 24th, Mexicans mix religion with pageantry, decorating their homes and visiting house-to-house seeking shelter, re-enacting the hardships of Mary and Joseph in Bethlehem. They are turned away by other families, innkeeper-style, and the candlelight procession continues. Marchers sing and say different prayers each night, until they are finally welcomed at the last house. That's the religious side of the Posadas -- meaning lodging or shelter.

But the other side is strictly frivolous. For sheer fun and to get rid of kiddie aggressions, there's the pinata, a suspened earthenware jar that the blindfolded children smack with sticks until it breaks, showering them with toys and candies. Nowadays a balloon covered with papier mache, tissue or tinsel, does the trick.

But set the paste-pot next to the phone; the guest list comes first. Indulge your culinary antiojitos (little whims) in rowdy good company.

If the people you're inviting know one another well enough to form a chain to spread the word, all the better.

Invite all the musicians you know and love, who can be counted on not only to drink and be merry but to provide after-dinner entertainment. For mood music, RECORDS AND TAPE LTD., 1239 Wisconsin Avenue NW, has a "Mariachi Oro y Plata" (gold and silver) LP for $5.99. Or if you're feeling rich, rent a whole mariachi band. Call the Mexican embassy (234-6000, and ask for Cesareo Manjarrez -- it helps if you speak Spanish, but even without the language you can line up his crew of nine strolling minstrels, Mariachi de LAS AMERICAS, to play in elaborate costumes for $200 an hour.

Dial a last-minute barkeep. The guys at Georgetown University's DELTA PHI EPSILON (337-9702) say a brother will mix, shake and pour for $25 "plus tips." Make sure they're familiar with margaritas.

Next, rustle up the food. A couple of hours on Saturday should do it. THE TUCSON CANTINA, 2605 Connecticut Avenue NW, offers a pint of guacamole dip for $7.49, burritos for $2.25 each and tamales at $1.25, and complete taco kits -- 20 tacos with onion, tomato, guacamole, cheese and beef filling -- for $22.45. It's probably a 20-minute wait, so cross the avenue to SHERRY'S LIQUORS and consider the tequila shelf. While Montezuma for under $6 would satisfy the tequila sunrise set, the salt-and-lime hot shots will appreciate the Prima Vera 101 for about $12. Live a little; you'll be cashing in on your hospitality at other people's New Year's Eves.

A most compatible duo, Dos Equis beer and tocos. Sherry's stocks the Mexican import at $4.99 a six-pack.

Swing onto Calvert Street and drive for three minutes, then look for a place to park south of the 18th Street border, near the OMEGA RESTAURANT (1856 Columbia Road) for another ten. Caramba! Of all the charms Adams-Morgan offers, plentiful parking is not one. True, the Omega is Cuban rather than Mexican, but a chicken enchilada is a chicken enchilada. They're $4.45 an order; scale down the numbers since each order includes two hefty enchiladas with plenty of meat, plus rice and black beans. Get out your pocket calculator and press on.

Appetizer inspiration: the chili con queso at LA FONDA, 1639 R Street NW. Catch them when the kitchen staff comes in, between 1 and 2, and bring your own bowl since they have no take-out implements on hand. For $10 they'll give you enough of the hot, melted cheese-and-peppers glop to serve 20. Plus, they'll throw in some chips.

Hot enough for you? To cool down 20 fiery palates, ice cream works better than flan. HAIGEN DAZS at Dupont Circle isn't far away, and the chocolate-chip beckons at $5 a quart, coffee at $4.50.

Pick up an aura of Mexico for your mantle or tree. THE PHOENIX in Georgetown has brightly colored ornaments (rocking animals $3) and wooden angels ($15.50). Tin or clay candelabra range from $6.50 to $60 to one gigantic colorful one in clay for $250.

Except for reheating later this evening, you're ready to roll. Next, get to work on your personalized pinata.Inflate a round balloon to 11" and tie. Apply four layers of newspaper strips, dipped in liquid starch or paste, leaving 3" x 3" uncovered at the stem for the opening. Allow time for your project to dry, then deflate the balloon and decorate without inhibition. Anything light, small and non-breakable can be packed inside, and the hole covered with crepe paper. Glue on streamers, tassles or cone-shaped newspaper points. Sprinkle with glitter or confetti. Paint in psychedelic or pastel hues or draw fantastical animal features and harness with string and tape so that your handiwork can be hung before it is smashed.

The pinata is to a Mexican Christmas what the stocking is to the American version, what the dreidel is to Hanukah, but it allows for more artsy innovation.