Now is the time for all good men to come to the aid of the party, and to come bearing balloons, party horns, confetti, crepe paper streamers, all the things it's easy to ignore once you're past the age of 7 and the annual birthday bash.

It's hard for people to stay stodgy when there are big clumps of ballons floating overhead in a helium heaven.

You can buy balloons on the spur of the moment from street sellers, and maybe even an inflated frog, but if you give 24-hours' notice, you can get 11-inch, blown-up balloons from Amusements, Unlimited . (593-2900).

They're $12 for the first dozen, and $10 for each additional dozen, when you pick them up at the company's warehouse, 4108 Howard Ave., Kensington, Md.

If you drive a Volkswagen, you might prefer to have them delivered, in which case it's $25 for the first dozen $10 for each additional dozen.

For $35 you can blow up your own; their party pack includes 100 9-inch ballons, a small helium tank (which must be returned), strings, tying discs, etc.

If you'd like to create a deep purple sky of balloons, try Ballon Bouquets, Inc. (785-1290), which carries ballons in colors that even include brown, silver and gold.

They'll deliver two dozen 9-inch baloons inside the Beltway for $24, with a $10 surcharge on evenings, weekends and holidays.

If you have endless lung power or a politician in residence, the Paper Store, 613 Massachusetts Ave. NW, will sell you a gross (144) of uninflated balloons for $6.75 or an inflated one for 50 cents.

They also have crepe paper streamers in assorted colors and prices, starting at 69 cents, and party horns to blow in your neighbor's ear for 26 cents.

Parties Unlimited . 14th and I Streets NW., will sell you an ounce of confetti for 40 cents. Unless you have a built-in vacuum system or a live-in maid, though, you might prefer to leave confetti to outdoor celebrations.

Indoors, you could wind your guests round with a roll of Stick Ups, long strips of paper bearing little stick-um figures of ducks, bears, geese, pigs, hearts, stars etc. You can buy one for 5 cents, or buy them by the foot.

If you don't want to use them to drape your guests, the individual figures would make unusual placecards. They're at the Written Word , 1365 Connecticut Ave. NW, or 1054 31st St.NW. The store also his lots of original inviations for everything from Luscious Lunch to Simple Supper.

But the most original thing would be to send out your invitations on T-shirts, with a request that your guests wear them to the party. The Silver Image in Georgetown, 3203 Grace St. NW (337-3705), will produce your inviation, illustration, or whatever on a T-shirt for prices ranging from $7 to $9 depending on the quantity.