An artist who likes people to walk all over his work

In their typically nonchalant manner, Bostonians are walking right over masterpieces of Western art - copies on concrete of works by artists like Degas, Renoir, Caravaggio, and others.

And no one's complaining.

They're all participants - often unknowingly - in the Hub's ''Boston Art Walk ,'' a six-month effort by artist Bob Guillemin, who has garnered a certain amount of fame under the name ''Sidewalk Sam.'' Although his works have been shown in museums and galleries - though sometimes under unusual circumstances - he prefers exhibiting on the street.

Mr. Guillemin's street work, however, has earned him considerable commercial success. The artist, who studied at the Ecole de Beaux Arts in Paris and eventually became a copyist at the Louvre, travels widely across the United States doing sidewalk masterpieces under the sponsorship of a wide range of commercial enterprises. He also specializes in something he calls ''community-pride murals,'' artworks incorporating landmarks, local themes, or both.

It's a curious mixture of business and art that has become a three-person business called Guillemin & Co.

This summer more than 50 of Guillemin's acrylic paintings will decorate Boston, most of them along the city's ''Freedom Trail,'' a path leading visitors through historic sites. In this he's backed by city and state agencies. Most of these works will be under business sponsorship, to the tune of $2,000 apiece (maintenance and corporate logo included).

Recently, Guillemin was at work on Boston Common near the busy Park Street subway station. His work for that day was a Revolutionary War Minuteman, a painting he completed with vigorous brushstrokes amid friendly tete-a-tetes with individuals from an ebbing and swelling audience of between 15 and 35. Then, underneath, in brilliant corporate colors, he added the logo of the company sponsoring the picture.

Guillemin makes no apologies for his financial success, his dealings with business, or for his down-to-earth method of operation. He remarks: ''The conditions are always right for art. There's no situation so mundane and poor that it isn't a beautiful environment for the human spirit.

''I want art to be part of a daily experience. Public art actually doesn't exist that much today. It's private art thrust into the public sector.''

As for Guillemin's success at mixing paint with commerce, he says: ''I (offer to) do something that's good for you, and you can pay me for it. That's a healthy way for art to act. Artists have to go out with a shovel over their shoulders and do some work.'' At the same time, he notes that ''90 percent of (the sidewalk art) I've done has never been paid for.''

Recently, Guillemin did one of his community-pride murals in Indianapolis to commemorate 100 years of downtown activity. It was sponsored by a shopping mall and will eventually be transferred to the Indianapolis Children's Museum. A larger-than-life-size Mona Lisa in a Portland, Ore., shopping mall wore away - along with its smile - in about a week, but sponsors were delighted at the heavy attention the exercise attracted in the news media.

Guillemin has done about a dozen works, mostly on sidewalks, for the Digital Equipment Corporation. According to Joseph Nangle, marketing and communications manager of Digital Business Centers: ''He's the consummate showman. We treat these as a happening, not as a freezable, holdable thing.'' Hence the tendency of the work Guillemin does for Digital to be literal washouts after the next rainstorm. Sidewalk Sam's mural depiction of ''25 Years of Digital in Chicago'' remains, however, in Chicago's Merchandise Mart Building.

Guillemin's ultimate goal? ''To do the Sistine Chapel ceiling on the sidewalk.''