On both sides of the street, signs advertise "Condominiums Available" and "Now Leasing Office Space." High-rise condominiums, towering office buildings and sleek mini-shopping centers with high-tech stores and trendy boutiques dot the landscape.

Until recently this stretch of Mass. Ave. between Harvard and Central Square was a self-contained neighborhood, with quiet restaurants and bars, its own movie theater and small, local businesses catering to the area's residents.

Since the real estate boom of the early 1980s, however, the condo developers and national chain stores have moved up from Harvard Square, slowly edging out the old way of life along Mass. Ave.

The pre-war apartment buildings are still there, and some small businesses still hold on to their leases, competing with the video and furniture stores for space. But while the old and the new seem to be peacefully coexisting, the neighborhood itself has taken on a different flavor, area business owners and community activists say.

"The whole character of Mass. Ave. is evolving," says Bobbi Bishop, director of marketing for Unihab Inc., which markets Bay Square Condominiums, one of the area's many new developments.

And while most people say that the changes are not for the worse, they add that the pace has quickened for this once-slow stretch between two of Cambridge's busiest areas. A new, high-tech way of life has moved in, with an upscale grocery store, a compact disc shop and futon vendors now lining the street.

Although Sally R. Alcorn of the Harvard Square Business Association says she doesn't think the neighborhood's character will be swallowed up, the number--and type--of new stores indicate the depth of the change.

Alcorn says that the area is still neighborhood-oriented. "Whenever you have a drugstore and a deli in the area, those are conveniences that residents are grateful for," she says.

It's just a question of what kind of conveniences residents need. Macaroni and cheese, no more. Now you can head over to Barsamian's to pick up a pound of Scottish smoked salmon for $26.50 or some rabbit pate for $9.58. Next stop: Videosmith, where local residents can drop off their Master-cards and rent the latest French film ($2.75 a day plus tax) to watch on their video cassette recorders.

But Alcorn says that the changes benefit everyone--big businesses and small, long-time residents and newcomers to the area. "The more life there is after 6 p.m. in a neighborhood, the better it is for the residents," she says.

And the more upscale, the better, according to store owners and residents.

"I don't see any opposition [to our new store] at all," says Marylou J. Sirois, a salesperson in the Furniture Store. "This is crafted furniture as opposed to a lot of mass-produced stuff," she says.

"The new stores are vastly less noisy and vastly better run than the [Orson Welles] theater was," says one resident who asked to remain anonymous. "The new stores are very sensitive to the needs of the neighborhood," she says, "in terms of noise, cleanliness, hygeine, safety and fire laws."

The pace of the neighborhood's development, although partially dictated by the booming real estate market of the early 1980s, has also been spurred by the evolution of Cambridge itself.

For example, when the Orson Welles Cinema, an independent movie theater located on the corner of Mass. Ave. and Dana St., burned down in the spring of 1986, it was eventually replaced by a host of new high-tech, upscale stores such as Videosmith, Digital Record, Toppers and The Furniture Store.