Leo Anderson -- on Mondays at noon a town crier, at other hours in the workweek a senior descriptive cataloguer at the Library of Congress -- was breezily speeding through the front courtyard of the Madison Building yesterday, dressed in 18th-century costume, ringing a hand bell and perched atop his Cannondale racing bicycle.

"Leo, what are you doing?" called a friend to the slender, 64-year-old cyclist.

"I'm at it again," he replied, giggling gleefully. "Hear ye, hear ye!"

In town crier costume of russet-colored wool suit, tricorn hat, white wig and granny glasses he sped in and out of tourist traffic.

"Who is that guy?" asked a bewildered woman.

"Leo Anderson. Up in processing," explained John Sullivan, a public information officer with the library.

"I mean what's he doing?"

"He's a town crier ..." "But what's he crying about?"

For the bewildered, the short answer: He's commemorating the 200th anniversary of the United States Constitution and stirring up interest in the library's current exhibition, "The American Solution: Origins of the United States Constitution." Usually Anderson delivers his bicentennial minutes without the Cannondale, but there was talk of using it on a regular basis -- it makes a great entrance.

HEAR YE! HEAR YE! We the people of the United States, in order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence ... Every Monday at noon (until mid-September), starting at the Neptune Plaza of the Jefferson Building and moving on to the courtyard of the Madison Building, Anderson strides into an arena of camera-toting tourists and sandwich-eating lunchers, rings his hand bell, and cries for a couple of minutes. His script is a bundle of photocopied pages, stapled together; his news is strictly 18th century, gleaned from the newspapers of that period:

A dancing school with Mr. Griffiths is being organized. Mr. Griffiths is a Dancing Master from New York and he will open the school this week at Mr. Enos Doolittle's large rooms in this city and continue the same thrice weekly ...

His bushy white eyebrows flicker emphatically. He bows. He waves his arms. He leans into the populace, working the crowd.

A few diehards walk right by. Others stand there grinning, arms akimbo, cameras around their necks.

The crier keeps crying:

... rates very reasonable ... a quantity of fresh lemons and prunes in boxes ... permit me to read you ...

"He's a ham," Sullivan said, explaining how he matched the gregarious Anderson with this Constitutional happening.

The days when the town crier was the main source of information for his often illiterate audience are long, long gone. These are the days of the photo op. Tourists love a good town crier. They circle around him, stand behind him, stare at him, snap pictures of him, and get autographs from him.

"Ohhh, you want to take a picture with me? Well, fine ... And where are you from? ... Where are you from? ... Where are you from?"

Less than a month after starting his new role, Anderson has become a mini-celebrity who pares his six-minute script to allow time for ad-libs. He has learned to stay sensitive to short attention spans, to pause during the roar of a passing truck. And sometimes, like yesterday, to anticipate problems.

As he and Sullivan headed down Pennsylvania Avenue for the second and final stop in the noontime crying, Anderson's eyes flickered and his head shook lightly. Trouble.

"Can we get 'em to turn that off?" he asked. In front of the Madison Building, two Blue Bird tour buses were idling out noise and pollution. He was being upstaged.