Certain street vendors sing in the rain. They are called umbrella vendors.

When it isn't raining, the 3,000-plus sidewalk salesmen of Washington will sell you almost anything else under the sun except liquor, vacation homes and most kinds of Volkswagens.

A handful of jonquils, for instance: $1. Indian cotton blouses? $5. Hot dogs are a dollar, halfsmokes $1.25. T-shirts are $4 for kids, $5 for others. Fifty cents buys your average apple, orange or banana. Calfskin pocketbooks, $25. Brass pinky rings, $2. Some of the curb merchandise (silver jewelry, for instance) really is handmade, but generally the hands were in Taiwan.

The croissants, however, are made in Rockville.

Bela K. Berty, 33, is out at 8 a.m. every morning at Dupont Circle to sell hot croissants from his Corner Gourmet cart (one of 14 scattered downtown). For lunch he rolls down to 19th and M Streets NW. "I'm stuck out here," he chuckled, eating a tomato he bought from a sidewalk colleague. "If I go inside to take a break, when I come out people are standing here waiting."

They are waiting, he says, either for plain croissants -- which 23-year-old Corner Gourmet Shops cofounder Nick Tillman points out are "each 26 hours in the making" at the Rockville bakery, and which others point out cost a dollar each -- or maybe for the Corner Gourmet "Stromboli" (meat-or vegetable-filled pita pockets), delivered to the corner stands just before lunch. Tillman said Corner Gourmet stands soon will have quiche and Swensen's sundaes. Tomorrow, the world.

Each of the District's 3,231 roving entrepreneurs paid either $25 (food) or $15 (other merchandise) to the District in 1981 for a license to peddle on the street. Their number, says the licenses and permits office spokeswoman, is rising slowly. It may soon decrease: The fees probably will increase dramatically next year if pending legislation goes through. The regulations already keep vendors six feet from each other, seven feet from the door of a business and always (theoretically) displaying their photo-bearing vending licenses.

Meanwhile vendors are concentrated by law and pedestrian tendencies into a number of downtown gauntlets. They include Connecticut Avenue above K Street NW, where you will find wicker-framed mirrors for $43, plus James Borland's big red Rare Print Wagon ($3 to $350) and Lee Fewell's brass buckle and handmade belt stand; around the Dupont Circle Metro stop exits; behind the Portrait Gallery between 9th and 10th Streets NW; a handful of corners on the east side of Wisconsin Avenue in Georgetown, the best place for late-night flower buys; and throughout the Mall, populated by a hundred converted panel trucks whose drivers hunker at Buzzard's Point every morning for prime space to sell their "PROPERTY OF WASHINGTON JAIL" T-shirts, genuine brown glass mugs labeled "WASHINGTON DC" along with pizza, ice cream and some pretty farfetched eggrolls.