CANTABRIGIANS USED TO GATHER IN DIMLY LIT CAFES TO CHAIN-SMOKE AND LAY PLANS FOR THE REVOLUTION. BUT TODAY, BRIGHT, CLEAN, TRANSPARENT COFFEE SHOPS COMMAND THE SQUARE.

Before rain washed the sidewalk outside Au Bon Pain this week, an artist covered the bricks with a chalk portrait of John Lennon. It was a throwback, perhaps, to the Au Bon Pain that Extension School Student Jordan R. Winer remembers.

"Twenty years ago, Harvard Square was really hip," Winer says. "Like, Bob Dylan spent a lot of time playing in all these folk-type cafes. Well now, no way. Now it's very posh, very fancy--Ann Taylor and so forth."

Winer is a self-appointed member of the Square's cafe culture--a sort of underground society that frequents the crowded hangouts where hermits cuddle in the corner with Hume, where chess masters with unkempt beards wage war for a dollar, where Jimi Hendrix impersonators make the cappuccino quiver with their electric guitars.

For them, what has come to represent so much of life around Harvard Square is changing, though, and regulars see Cambridge's cafe culture declining as trendy boutiques fill what used to be the folksy Square.

While first-years still zip from the Yard to slam late-night coffees at Au Bon Pain and a few upperclass students still hide behind books in Cafe Pamplona, many have noticed the dearth of younger patrons.

And coffee-drinkers and employees alike are starting to worry that the Square's traditional haven for studies and socializing is becoming too upscale for its own good.

Take Au Bon Pain, the Square's colossal central coffee shop. The French words aren't too hard to pronounce, really. But the less ambitious have taken to labeling the cafe "ABP." After all, these are the '90s, and short attention spans and busy lives have reduced rules of pronunciation to a single concept: the simpler, the better.

To match the coffee shop's abbreviated name, recent renovations have altered the atmosphere in Au Bon Pain. It's sleeker, a bit less cramped and definitely cleaner.

Today's "ABP" is all fluorescent lights and faux marble tables. The cafe added a sunroom-style front section, jazzed up its designer food display case and imported coffee beans from its neighbor and cafe rival, The Coffee Connection.

But these changes for modern convenience have taken something fundamental from the old Au Bon Pain ambience, Winer explains.

"Au Bon Pain isn't comfortable to go to," he says. "It's kind of like McDonald's. Everything's sort of computerized."

Au Bon Pain isn't the only Harvard Square coffee shop that has transformed physically in recent years. Winer has similar complaints about Cafe Algiers, which closed temporarily, under-went a complete refurbishment and reopened with a new look last fall.

The old Cafe Algiers, Winer recalls, "was the last really `cafe' type cafe in the area. Everyone--undergrads, grads, adults--went there. It wasn't a big deal if you spent a couple hours there with one coffee."

Last year's renovation at the Brattle Street shop added seating in a second-floor loft, eliminated the lower floor and padded the prices. On the Cafe Algiers menu today, cappuccino costs $2.75.